# Mastermind meets the Dolmar 7900



## Mastermind (Jan 16, 2012)

Here's a few pics of a build I'm working on.

This is a nice clean saw. It had a Chinese top end and only 140psi... 

We're gonna fix that though. 





New OEM 79cc jug and new light weight slab sided piston.....yeah baby!!! 





It look to me like the designers wanted to try to do something to help the small case size on this saw. There's lots of potential here IMHO. 












I'll cut the squish band flat and build a popup in this one.

That's it for now. A bunch of work showed up here today for one of my local guys that held me up a bit. We'll get back on it in the AM though.


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## Stihl n Wood (Jan 16, 2012)

Master mind, what type of piston is that? Dumb question but are you making your own windows in that piston? Or do dolmars not have windows? I'm not familiar with dolmars what so ever as you can see. The jug looks like it has alot of potential though. Lots of meat by the looks.. happy shaving!!


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## Mastermind (Jan 17, 2012)

Stihl n Wood said:


> Master mind, what type of piston is that? Dumb question but are you making your own windows in that piston? Or do dolmars not have windows? I'm not familiar with dolmars what so ever as you can see. The jug looks like it has alot of potential though. Lots of meat by the looks.. happy shaving!!



That's a factory piston for the 7900. It's the latest design for that saw. Lighter and with a different shape.....no windows.


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## chopperfreak2k1 (Jan 17, 2012)

that's a weird lookin piston. can't wait to see what ya do here Randy!


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## bryanr2 (Jan 17, 2012)

I'm watching this one extra close as I have the Makita 6401, the oem kit in a box, the HD filter, and black cover. The saw needs a sticker.


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## Terry Syd (Jan 17, 2012)

Good looking piston to get around all the shrouding of the lower transfers. - I never figured out why guys would put ports in pistons when the ports would be above the bottom of the cylinder at BDC.


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## Mastermind (Jan 17, 2012)

Terry Syd said:


> Good looking piston to get around all the shrouding of the lower transfers. - I never figured out why guys would put ports in pistons when the ports would be above the bottom of the cylinder at BDC.



I don't get that either Terry. In order for a windowed piston to be of use the lowers would need to be moved way the heck up the walls.


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## Andyshine77 (Jan 17, 2012)

Looks like a fine test subject. I'd say it's an 05 or 06 model. The oil lines will be black and the filter cover won't have the prefilter mesh screen. She will likely leak oil with the old black lines, but as long as it oils the bar properly it's fine. I personally haven't seen any performance difference with the HD filter. Don't go crazy with your porting numbers, blow down is your friend as well as intake duration. 

Have fun with the build.


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## Andyshine77 (Jan 17, 2012)

Terry Syd said:


> Good looking piston to get around all the shrouding of the lower transfers. - I never figured out why guys would put ports in pistons when the ports would be above the bottom of the cylinder at BDC.





Mastermind said:


> I don't get that either Terry. In order for a windowed piston to be of use the lowers would need to be moved way the heck up the walls.



Precisely.


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## bcorradi (Jan 17, 2012)

I'm curious to see how it works out for you. All of the good builders that I know say they can get more out of a 440 and a 372 than they can out of a 7900.


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## Andyshine77 (Jan 17, 2012)

bcorradi said:


> I'm curious to see how it works out for you. All of the good builders that I know say they can get more out of a 440 and a 372 than they can out of a 7900.



I'd say it's easier to build 440/372 than a 7900, but in the right hands the 7900's can really come alive.


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## bcorradi (Jan 17, 2012)

Andyshine77 said:


> I'd say it's easier to build 440/372 than a7900, but in the right hands the 7900's can really come alive.


Ya your probably right vs stock. However, I would think it would be at least a 1/2 step ahead once ported vs the 440/372 and that isn't the case from the people I talk to. It is a cool/formidable saw in stock form nonetheless.


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## Andyshine77 (Jan 17, 2012)

bcorradi said:


> Ya your probably right vs stock. However, I would think it would be at least a 1/2 step ahead once ported vs the 440/372 and that isn't the case from the people I talk to. It is a cool/formidable saw in stock form nonetheless.



Most of the time you're likely right, but the EC 7900's seem to be quite strong. 

<iframe width="420" height="315" src="http://www.youtube.com/embed/KrOKQUy24Q8" frameborder="0" allowfullscreen></iframe>


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## bcorradi (Jan 17, 2012)

Thats a good running saw. Heck who knows maybe mastermind will come up with a recipe that will turn out great and I wish him the best.


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## Terry Syd (Jan 17, 2012)

I figure one of the limits on power of the 7900 is the dinky 17mm carb. Probably why Andy made the emphasis on intake duration.

I've got four C3M carbs sitting here and I just might try butchering one up to see if I can open it up to 18-19mm. If it worked, I could use it on my 365BB, but it would also work on the 7900. Sure wish I had a lathe, using the Dremel is gonna be down right ugly.


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## bcorradi (Jan 17, 2012)

Terry Syd said:


> I figure one of the limits on power of the 7900 is the dinky 17mm carb. Probably why Andy made the emphasis on intake duration.
> 
> I've got four C3M carbs sitting here and I just might try butchering one up to see if I can open it up to 18-19mm. If it worked, I could use it on my 365BB, but it would also work on the 7900. Sure wish I had a lathe, using the Dremel is gonna be down right ugly.



Ya you could be right, but one of the guys I know had no problem drilling out carbs and experimenting with different carbs, etc. I'm not saying that there isn't very high potential...i'm just relaying info from people I have talked to. It would be awesome if a person could come up with a good recipe on the 7900 because it is a great saw.


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## Terry Syd (Jan 17, 2012)

I think I may bite the bullet and go for a WJ carb on my 365BB. I can clock the intake manifold to fit the carb and then use some parts from a 385 to make up a filter for it. That would give me a 19mm carb off of a 066. I wonder if the 7900 would be able to do something similar.


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## Andyshine77 (Jan 17, 2012)

Terry Syd said:


> I figure one of the limits on power of the 7900 is the dinky 17mm carb. Probably why Andy made the emphasis on intake duration.
> 
> I've got four C3M carbs sitting here and I just might try butchering one up to see if I can open it up to 18-19mm. If it worked, I could use it on my 365BB, but it would also work on the 7900. Sure wish I had a lathe, using the Dremel is gonna be down right ugly.



If I recall correctly the Walbro HD 12 carb that came on the 372 will bolt right in as well, not sure about the venturi size though.


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## Terry Syd (Jan 17, 2012)

The Walbro is actually a bit smaller than the Zama. Walbro is 16.67mm and Zama is 17mm.

I would prefer a straight bolt on mod, I'm not keen on cobbling up things up to get them to fit. However, it is just a firewood saw not a production saw, so if things rattle loose I can always walk back to the shed.


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## Andyshine77 (Jan 17, 2012)

Terry Syd said:


> The Walbro is actually a bit smaller than the Zama. Walbro is 16.67mm and Zama is 17mm.
> 
> I would prefer a straight bolt on mod, I'm not keen on cobbling up things up to get them to fit. However, it is just a firewood saw not a production saw, so if things rattle loose I can always walk back to the shed.



I was thinking the HD carb may actually have a smaller venturi, it's been some time since I looked. I agree a real work saw needs to be reliable, so a bolt on is preferred in this build I'm sure.


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## AUSSIE1 (Jan 17, 2012)

Terry Syd said:


> I figure one of the limits on power of the 7900 is the dinky 17mm carb. Probably why Andy made the emphasis on intake duration.
> 
> I've got four C3M carbs sitting here and I just might try butchering one up to see if I can open it up to 18-19mm. If it worked, I could use it on my 365BB, but it would also work on the 7900. Sure wish I had a lathe, using the Dremel is gonna be down right ugly.



Mount your carb in a cordless drill.

Bolt....washer.....carb......washer.....nut.....drill!


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## Terry Syd (Jan 17, 2012)

Hmm, I've got a cheap Chinese drill press ($80) that I might chuck it up in, then stick the Dremel up inside while its spinning and hog it out - bush engineering at its finest.

Crikey Al, I'm actually thinking of doing this!


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## AUSSIE1 (Jan 17, 2012)

Terry Syd said:


> Hmm, I've got a cheap Chinese drill press ($80) that I might chuck it up in, then stick the Dremel up inside while its spinning and hog it out - bush engineering at its finest.
> 
> Crikey Al, I'm actually thinking of doing this!



Chainsaw file with the end cut off will remove plenty. You could lay down the drill press.

Be careful you don't go too far and pop into ports. I did and it took awhile to find it. Just pressurise the carb under water. If you do pop through, nail polish is a great sealer.


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## Terry Syd (Jan 17, 2012)

Convert the choke valve to a throttle valve, then take some tin and make a bigger choke valve - yep, it's do-able. 

Poor Randy, he'll come back to his build thread and find a bunch of Aussies have been crapping on while he was sleeping.


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## 385XP (Jan 17, 2012)

Andyshine77 said:


> If I recall correctly the Walbro HD 12 carb that came on the 372 will bolt right in as well, not sure about the venturi size though.


I think you might be on to something with the walbro carbs. I beleve all the issuses ive had with the 7900 not want to restart when warm is a result of the zama carb. I may give the 7900s another try when they become available again.


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## porsche965 (Jan 17, 2012)

Should be a good thread. Subscribed.


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## o8f150 (Jan 17, 2012)

Mastermind said:


> Here's a few pics of a build I'm working on.
> 
> This is a nice clean saw. It had a Chinese top end and only 140psi...
> 
> ...



looks like it should be a smoking saw when you are done,, what the hell am i saying,,any saw that you have built has been a smoking saw,,but i bet that pos dolmar won't keep up with my 372


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## deye223 (Jan 17, 2012)

Subscribed


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## deye223 (Jan 17, 2012)

o8f150 said:


> looks like it should be a smoking saw when you are done,, what the hell am i saying,,any saw that you have built has been a smoking saw,,but i bet that pos dolmar won't keep up with my 372



opcorn:


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## blsnelling (Jan 17, 2012)

I don't know how he does it, but Copsey can build a 7900 that will smoke a 372. Seeing is believing. Typical porting numbers go out the window with the 7900.


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## Mastermind (Jan 17, 2012)

Andyshine77 said:


> Looks like a fine test subject. I'd say it's an 05 or 06 model. The oil lines will be black and the filter cover won't have the prefilter mesh screen. She will likely leak oil with the old black lines, but as long as it oils the bar properly it's fine. I personally haven't seen any performance difference with the HD filter. Don't go crazy with your porting numbers, blow down is your friend as well as intake duration.
> 
> Have fun with the build.



I checked numbers on the new top end last night. It will end up with 162 duration after machining the jug. It has 30 degrees blowdown now. :msp_w00t:



bcorradi said:


> I'm curious to see how it works out for you. *All of the good builders *that I know say they can get more out of a 440 and a 372 than they can out of a 7900.



Well I'm out.... :msp_sad:



o8f150 said:


> looks like it should be a smoking saw when you are done,, what the hell am i saying,,any saw that you have built has been a smoking saw,,but i bet that pos dolmar won't keep up with my 372




Speaking of your 372......I'll box it up today. It's pushing 175psi and is very strong. I've ran several tanks of fuel through it and really like the way it turned out. I do apologize for having it so long, though I did get some great info out of it and the other one I built along with it.


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## Mastermind (Jan 17, 2012)

blsnelling said:


> I don't know how he does it, but Copsey can build a 7900 that will smoke a 372. Seeing is believing. Typical porting numbers go out the window with the 7900.



It's the elbow grease. He has a special blend that is Dolmar approved. :msp_wink:


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## bigredd (Jan 17, 2012)

That is definately the 7900 I sold to a fellow AS Member. Very interested in seeing how it turns out.


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## 8433jeff (Jan 17, 2012)

I love this channel.


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## importjunk (Jan 17, 2012)

Subscribed


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## c5rulz (Jan 17, 2012)

Call me ears.opcorn:


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## cutmaster (Jan 17, 2012)

*Yea Man!*



blsnelling said:


> I don't know how he does it, but Copsey can build a 7900 that will smoke a 372. Seeing is believing. Typical porting numbers go out the window with the 7900.



I gotta get a hold of EC ( Copsey ) again myself, I want him to build up all 26 of our PS7900's!
Brad, if you can't reach Copsey for the next 3 months it's your own fault, you sent me to him in the first place! Gotta get through all this court B.S. first though


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## russhd1997 (Jan 17, 2012)

Another Dolmar porting thread. You got my interest. opcorn:


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## timmcat (Jan 17, 2012)

Where's the next report?opcorn:


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## Mastermind (Jan 17, 2012)

timmcat said:


> Where's the next report?opcorn:



I've been tuning on my lathe all damn day. :msp_mad:

Cheap Chinese bastards....... I feel sooooo dirty. 

I'm replacing the slides on the carriage and polishing the ways and jibs. The little buggers can be very accurate, but some serious tuning must be done.


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## o8f150 (Jan 17, 2012)

Mastermind said:


> Speaking of your 372......I'll box it up today. It's pushing 175psi and is very strong. I've ran several tanks of fuel through it and really like the way it turned out. I do apologize for having it so long, though I did get some great info out of it and the other one I built along with it.



i feel so used and abused now,,, we all know you just wanted to cut some firewood for yourself:hmm3grin2orange::hmm3grin2orange::hmm3grin2orange:
it not a problem randy,, glad you got some info with it,, that makes it worth the wait


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## Mastermind (Jan 17, 2012)

o8f150 said:


> i feel so used and abused now,,, we all know you just wanted to cut some firewood for yourself:hmm3grin2orange::hmm3grin2orange::hmm3grin2orange:
> it not a problem randy,, glad you got some info with it,, that makes it worth the wait



I counted the saws in my shop a little while ago. There's 38 of em. 

If I hadn't needed the shelf space I woulda kept it longer. :hmm3grin2orange:


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## o8f150 (Jan 17, 2012)

Mastermind said:


> I counted the saws in my shop a little while ago. There's 38 of em.
> 
> If I hadn't needed the shelf space I woulda kept it longer. :hmm3grin2orange:



if wanted to keep it then it must have turned out good,, not bad for a 225.00 saw:biggrin::biggrin: yes i know,, just rub it in:hmm3grin2orange::hmm3grin2orange:


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## Hedgerow (Jan 17, 2012)

opcorn:


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## wendell (Jan 17, 2012)

o8f150 said:


> looks like it should be a smoking saw when you are done,, what the hell am i saying,,any saw that you have built has been a smoking saw,,but i bet that pos dolmar won't keep up with my 372



Time to go back to your snackies. :msp_thumbdn:


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## Hedgerow (Jan 17, 2012)

wendell said:


> Time to go back to your snackies. :msp_thumbdn:



Hey Wendell, I need to borrow your Makita... Not for long though... And I promise to put it back together when I'm done with it...
:hell_boy:


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## Isna (Jan 17, 2012)

opcorn:


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## Andyshine77 (Jan 17, 2012)

Mastermind said:


> I checked numbers on the new top end last night. It will end up with 162 duration after machining the jug. It has 30 degrees blowdown now. :msp_w00t:



Duration sounds good, I'd like a few degrees less but you're OK. You could also get away with a LITTLE less blowdown. Squish can be a bit tight with theses saws as well, they seem thermally efficient as they don't like to heat up, even with pretty high compression.


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## wendell (Jan 17, 2012)

Hedgerow said:


> Hey Wendell, I need to borrow your Makita... Not for long though... And I promise to put it back together when I'm done with it...



I'll get back to you on that.


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## mweba (Jan 17, 2012)

wendell said:


> I'll get back to you on that.



If you let him borrow it......is ear protection included?


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## Hedgerow (Jan 17, 2012)

mweba said:


> If you let him borrow it......is ear protection included?



Awe... That saw is quiet compared to my 372.... Wait till I let you run that one... Bring yer ear plugs... :hmm3grin2orange:


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## Mastermind (Jan 17, 2012)

Well fellers I lost a whole day due to my lathe taking a crap on me. It took a while to find it but one of the slides on the carriage had cracked. This caused it to chatter badly. I got it fixed and re-tuned......finally. :msp_thumbdn:


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## Jakers (Jan 18, 2012)

Mastermind said:


> I counted the saws in my shop a little while ago. There's 38 of em.
> 
> If I hadn't needed the shelf space I woulda kept it longer. :hmm3grin2orange:



with another one on the way :msp_thumbup:


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## cutmaster (Jan 18, 2012)

*Another One Bites the Dust ~*

This is our second Dolmar PS 7900 that got stuck-up....
This one we even opened up the muffler a little bit and ran it a tad rich....
Is running 5 gallons a day through these saws causing this?
View attachment 218239

:msp_mad:View attachment 218240

View attachment 218241

:taped:View attachment 218242


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## srcarr52 (Jan 18, 2012)

cutmaster said:


> This is our second Dolmar PS 7900 that got stuck-up....
> This one we even opened up the muffler a little bit and ran it a tad rich....
> Is running 5 gallons a day through these saws causing this?
> View attachment 218239
> ...



Having scoring on even the intake side suggests that it was run with a low oil or no oil mix. The combustion chamber and spark plug have good color so it was not a lean seizure. I bet that cylinder can be saved with muratic acid.


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## nmurph (Jan 18, 2012)

cutmaster said:


> This one we even opened up the muffler a little bit and ran it a tad rich....



Did you have it four-stroking good at wide open throttle?


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## Jacob J. (Jan 18, 2012)

srcarr52 said:


> Having scoring on even the intake side suggests that it was run with a low oil or no oil mix. The combustion chamber and spark plug have good color so it was not a lean seizure. I bet that cylinder can be saved with muratic acid.



Maybe the gas was a bit stale?

Cutmaster- do you have a bulk tank for gas that you use? People with bulk tanks sometimes have the gas sit a while and it starts to go stale. 

Remember too- Stabil and similar products help to keep gas chemically stable but they do not protect or preserve the octane rating of gas.
Gas starts losing its' octane rating steadily when its stored.


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## Hedgerow (Jan 18, 2012)

cutmaster said:


> This is our second Dolmar PS 7900 that got stuck-up....
> This one we even opened up the muffler a little bit and ran it a tad rich....
> Is running 5 gallons a day through these saws causing this?
> View attachment 218239
> ...



Plug looks good... But odd that damage would be done on the intake side...:msp_confused:


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## blsnelling (Jan 18, 2012)

Do you fire them up in that MN cold and throw them straight in the cut? Do you retune for the cold weather?


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## 8433jeff (Jan 18, 2012)

Only the second day of winter here, Brad; bet its been colder there than the lower half of MN.
If hes north of that, then maybe. How do you run five gallons of fuel through it a day, isn't that like 15 tanks?


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## srcarr52 (Jan 18, 2012)

blsnelling said:


> Do you fire them up in that MN cold and throw them straight in the cut? Do you retune for the cold weather?



Good point... could be cold seizing. 



8433jeff said:


> Only the second day of winter here, Brad; bet its been colder there than the lower half of MN.
> If hes north of that, then maybe. How do you run five gallons of fuel through it a day, isn't that like 15 tanks?



5 gallons I think is somewhere between 15-20 tanks... that is a lot of run time and many fill ups for someone to put raw fuel in or to mess up on the ratio.


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## cutmaster (Jan 18, 2012)

srcarr52 said:


> Having scoring on even the intake side suggests that it was run with a low oil or no oil mix. The combustion chamber and spark plug have good color so it was not a lean seizure. I bet that cylinder can be saved with muratic acid.



Srcarr, it's the exhaust side, arrow points to muffler as does the ring gap.
Unless all these I purchased were put together during OctoberFest!:msp_confused:


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## cutmaster (Jan 18, 2012)

nmurph said:


> Did you have it four-stroking good at wide open throttle?



mmurph
yes, at no load WOT it 4-stroked pretty good.


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## nmurph (Jan 18, 2012)

How are you tuning these saws?


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## cutmaster (Jan 18, 2012)

Jacob J. said:


> Maybe the gas was a bit stale?
> 
> Cutmaster- do you have a bulk tank for gas that you use? People with bulk tanks sometimes have the gas sit a while and it starts to go stale.
> 
> ...



Jacob,
we do use a steel 55 gallon drum.
We use Husqvarna XP Professional Performance 2 Cycle Oil mixed at 48:1
with Sunoco 260 GTX unleaded - no oxygenates and no metallic additives.
1 Gallon Husqvarna XP Professional Performance 2 Cycle Oil
added to 48 Gallons of Sunoco 260 GTX unleaded.


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## srcarr52 (Jan 18, 2012)

cutmaster said:


> Srcarr, it's the exhaust side, arrow points to muffler as does the ring gap.
> Unless all these I purchased were put together during OctoberFest!:msp_confused:



The locator pin is in the middle of the exhaust port? That sounds like a wonderful way to snag a ring.


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## cutmaster (Jan 18, 2012)

blsnelling said:


> Do you fire them up in that MN cold and throw them straight in the cut? Do you retune for the cold weather?



Brad,
no never - we always start the saws in the sawmill shop, it's about 50 degrees in there without the heat on, my 2 sons and I always start the morning out like this:
We have breakfast, while my wife makes our lunches for the day we go out into the sawmill, check the saws out, fill them up with fuel and bar oil, sharpen the chains, the cut up slabwoord ( the thin bark left over from the sawmill from the day before ) push it all outside with the skidsteer, then I use my big bucket loader and dump it all across the road where people snatch it up like it's money.
Then it's back in the house to get our lunches then we head out into the woods, - resharpen the chains, fill everything back up start the saws for 5 to 10 minutes while I hollar at the boys as to what I need each of them to do, then we cut trees down until we can't move, then I jump in the skidder to clear the area while my boys continue cutting.

Here is the strangest thing:
The first Dolmar I blew up, while my 2 sons continued to run their Husqvarna 372XP's.
Same bar oil, same gas mix, same everything.
This saw is the second PS 7900 to blow up, my youngest son used this on.
I went back to using my Husqvarna 395XP, my oldest running his Husqvarna 372XP.
Again, fueled and oiled from the same containers, everything the same.
The only common thing here that I can see is Husqvarna vs Dolmar.
I am not in anyway shape or form bashing Dolmar!
I am stating the facts to all of you to help myself out here, I made a large purchase of 7900's this past fall and I'm asking for you all to help me figure out what is going on with these Dolmar Saws.

Steve


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## nmurph (Jan 18, 2012)

cutmaster said:


> mmurph
> yes, at no load WOT it 4-stroked pretty good.



You do realize that these saws have a limited coil? Four stroking at WOT sounds like you are hitting the limiter. They will do this and still be too lean.


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## Dan_IN_MN (Jan 18, 2012)

cutmaster said:


> Jacob,
> we do use a steel 55 gallon drum.
> We use Husqvarna XP Professional Performance 2 Cycle Oil mixed at 48:1
> with Sunoco 260 GTX unleaded - no oxygenates and no metallic additives.
> ...



I'm not sure if this is a red flag or not....Are you mixing the whole 55 gallons all at once? Is this a common thing to do? What is the chance of the oil settling over time or not being mixed thoroughly with the gas? Where are you in located in MN?


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## thomas1 (Jan 18, 2012)

Holy thread derail, Batman!


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## Mastermind (Jan 18, 2012)

Derail away. 

I just hope you figure out what has been killing your saws. What nmurph said about the limited coil is what my money's on. I just ran a stock one that was bouncing off of the limiter badly. 

I'm almost done with the first 7900 with two more to go. Everything that could happen to slow a day up has happened here today. My wife's van took a crap, local guys have been in and out all day, the phone has been ringing off the hook.............I'll get done someday.


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## cutmaster (Jan 18, 2012)

nmurph said:


> How are you tuning these saws?



Since this was the second 7900 that we were using we were now aware the first saw had a problem the we never could find out " why "
This saw I thought we had tuned up rich and perfect, the original hole on the muffler seemed small for a 79cc saw, it was a 14mm hole, I opened up that same hole to 17mm.
Then pulled the caps off the carb, band new out of the box I turned out both carb adjustment screws out 1/2 turn each, I put a tach on it and revved it lightly to 6751 rpm, once the saw was hot I turned it off and adjusted the I started the saw and adjusted the dle speed to 2500 rpm, I then turned the low speed carb screw in until it started to surge. I then backed that screw out until the engine started to load up. I split the difference between the lean and rich setting, say 2 o'clock was lean and 10 o'clock was rich, I ended up at 12 o'clock, I then went out about 1/8 turn and re-adjusted my idle speed to 2500 rpm. I then went to WOT and hit the kill switch, tach said 13,884, I backed out the high speed screw 1/4 turn, started the saw and went to WOT and hit the kill switch, tach said 11,414 rpm, it sounded great at that point, I then started the saw with the tach still attached and started a cut through a 15" dia red oak log, I dug it in slightly and hit the kill switch, tach said 8112 RPM. I pulled the spark plug and it looked rich, I replaced the spark plug with a new one, made 4 cuts and pulled the spark plug again, it looked rich.
This is how I left it until it blew......
I am no pro saw tuner, so if I did anything wrong here please let me know, I tune all my saws this same way and have for roughly the last 15 years, ever since I bumped into a chainsaw tach!!

Steve


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## o8f150 (Jan 18, 2012)

thomas1 said:


> Holy thread derail, Batman!



thats what i was thinking


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## blsnelling (Jan 18, 2012)

11,400 is WAY too rich for a 7900. You need to get the saw good and warm. Start rich. Have someone else hold the tach. Go WOT and lean it out until you see 13,500 or until it bumps the rev limiter. From there, you'll have to tune it in the wood. It should run perfectly clean in the cut, but slightly 4-stroke when you let off the load. However, as already mentioned, it's VERY easy to think it's 4-stroking when it's actually hitting the limiter. This is why I despise rev limited coils and one reason that I just can't fall in love with a 7900. That, and the fact that they look like an AMC Pacer!!!


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## steve316 (Jan 18, 2012)

*amc pacer*

Brad that that amc pacer shoy was like adagger to the heart Steve


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## blsnelling (Jan 18, 2012)

steve316 said:


> Brad that that amc pacer shoy was like adagger to the heart Steve



Even in the right colors


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## cutmaster (Jan 18, 2012)

blsnelling said:


> 11,400 is WAY too rich for a 7900. You need to get the saw good and warm. Start rich. Have someone else hold the tach. Go WOT and lean it out until you see 13,500 or until it bumps the rev limiter. From there, you'll have to tune it in the wood. It should run perfectly clean in the cut, but slightly 4-stroke when you let off the load. However, as already mentioned, it's VERY easy to think it's 4-stroking when it's actually hitting the limiter. This is why I despise rev limited coils and one reason that I just can't fall in love with a 7900. That, and the fact that they look like an AMC Pacer!!!


Brad, 13,500 RPM is where the first one was set at, and that saw looks just like this one.....
I'm willing to try the EC unlimited coil trick - but if the next 7900 end up like these 2 - I'm going to dump the rest off on ebay and run to the hills!

A Pacer, c'mon Brad, A Pacer?? Dude that's gonna hurt for weeks on end!!!
Ahhhh!!!! 

Steve


----------



## Hedgerow (Jan 18, 2012)

Brad??? Why have you not found your way around that stupid coil yet???
Get busy you slacker!!!:msp_sneaky:


----------



## blsnelling (Jan 18, 2012)

The truth hurts sometimes:hmm3grin2orange:


----------



## blsnelling (Jan 18, 2012)

Hedgerow said:


> Brad??? Why have you not found your way around that stupid coil yet???
> Get busy you slacker!!!:msp_sneaky:



Yes, I did it once. Not worth the hassles. If I were to run another, I'd probably stick with the stock coil and just tune in the cut.


----------



## Buffhunter (Jan 18, 2012)

Mastermind said:


> Derail away.
> 
> I just hope you figure out what has been killing your saws. What nmurph said about the limited coil is what my money's on. I just ran a stock one that was bouncing off of the limiter badly.
> 
> I'm almost done with the first 7900 with two more to go. Everything that could happen to slow a day up has happened here today. My wife's van took a crap, local guys have been in and out all day, the phone has been ringing off the hook.............I'll get done someday.



Man don't these people know you have a 562 waiting to be molested?????? The nerve of some people. LOL


----------



## cutmaster (Jan 18, 2012)

manyhobies said:


> I'm not sure if this is a red flag or not....Are you mixing the whole 55 gallons all at once? Is this a common thing to do? What is the chance of the oil settling over time or not being mixed thoroughly with the gas? Where are you in located in MN?


Not a chance, I'm 11 miles north of mora, fuel is at the raceway in princeton 33 miles 1 way, we fill 16 gallons of fuel add 1 gallon oil and add 32 gallons of fuel, sloshes back and forth - bouncing up and down these crappy old logging roads in the back of an F550 with a liftgate for 33 miles, the drum has to sit for at least 8 hours prior to opening unless you want to get covered in fuel..... smells good for sure, eyes water and all that good stuff.


----------



## cutmaster (Jan 18, 2012)

blsnelling said:


> Even in the right colors



Ok that's it, that's it, i've had all I can take, there's only so much a guy can take and this is way over the line!

I'm going to have to Buy a bunch of Stihl saws and have you work your magic on them Brad!
So tell your wife you'll see her again sometime this summer!:hmm3grin2orange:


----------



## nmurph (Jan 18, 2012)

blsnelling said:


> Even in the right colors



Your car matches your motorcycle


----------



## Ductape (Jan 18, 2012)

At least he chose the Pacer X....... the *cough, cough* performance version. :cool2:


----------



## Hedgerow (Jan 18, 2012)

Ductape said:


> At least he chose the Pacer X....... the *cough, cough* performance version. :cool2:



Hmmm... The pacer that outruns the corvette... 
Just sayin...:msp_sneaky:


----------



## nmurph (Jan 18, 2012)

Cut, I understand what you were trying to accomplish by cutting the saw off in mid cut. But the tach is reading the RPM at the time the time the coil fires the last revolution or two. The saw may have already bumped the limiter and been on its way down when you pulled the plug and got the reading. Another thing to remember is that reading the plug is not an exact science, and most people make the mistake of looking at the area around the electrode.
I slowly adjust mine up against the limiter as seen on the tach. Then I back off a 1/8 turn or so and check it in the wood at Brad mentioned, listing for four-stroking and cleaning up in the cut.


----------



## Jacob J. (Jan 18, 2012)

Ductape said:


> At least he chose the Pacer X....... the *cough, cough* performance version. :cool2:



A good friend of our family had the Pacer X, but his was the silver and blue one. He had the open hatchback too. Five of us loaded up in that thing 
for a road trip. I was six and I spent the entire time in the hatchback. A 26-hour drive to South Dakota.


----------



## parrisw (Jan 18, 2012)

The only way to tune a limited ignition is in the wood, IMHO. 

I'll buy one of your blown up 7900's.


----------



## blsnelling (Jan 18, 2012)

nmurph said:


> Your car matches your motorcycle



Believe it or not, I thought about posting that pic


----------



## cutmaster (Jan 18, 2012)

nmurph said:


> Cut, I understand what you were trying to accomplish by cutting the saw off in mid cut. But the tach is reading the RPM at the time the time the coil fires the last revolution or two. The saw may have already bumped the limiter and been on its way down when you pulled the plug and got the reading. Another thing to remember is that reading the plug is not an exact science, and most people make the mistake of looking at the area around the electrode.
> I slowly adjust mine up against the limiter as seen on the tach. Then I back off a 1/8 turn or so and check it in the wood at Brad mentioned, listing for four-stroking and cleaning up in the cut.



Ok, I get all that,
what I don't get is " in the wood " tuning, how much pressure vs what rpm stuff.
Off the top of my head I believe the manual says 9500 RPM ( in the wood I would think )
but, at what pressure on the saw? I mean I can dig the dawgs in and have the saw turn 9500 RPM, but I know it will blow up on a lighter cut. So are we talking 9500 RPM in the wood with say no pressure on the saw?


----------



## blsnelling (Jan 18, 2012)

Forget actual RPM numbers here. Your simply listening for the saw to 4-stroke when you let off in the cut, and then instantly clean back up once put back under load. I have a thread somewhere that demostrates this. There are others as well. Matter of fact, my bud Andyshine77 demos it with a 7900. Maybe someone will have a link.


----------



## cutmaster (Jan 18, 2012)

parrisw said:


> The only way to tune a limited ignition is in the wood, IMHO.
> 
> I'll buy one of your blown up 7900's.



parrisw,
I'll sell you one but I have to warn you; Dolmar 7900's will flip you right over the top of a large tree laying on the ground such as the tree in your pic, I've had such good luck with these bad boys using any other saw is like cutting trees with a hack saw! So get your wallet out!
No really, I don't know what in the world is going on with all of mine, all of them are 2008 models.
Don't know if that is my issue or what......
By 2008 being an issue I am saying they had been sitting brand new in a warehouse for years, not that 2008 was a bad year...


----------



## cutmaster (Jan 18, 2012)

blsnelling said:


> Forget actual RPM numbers here. Your simply listening for the saw to 4-stroke when you let off in the cut, and then instantly clean back up once put back under load. I have a thread somewhere that demostrates this. There are others as well. Matter of fact, my bud Andyshine77 demos it with a 7900. Maybe someone will have a link.



Ah ha! now I see said the blind man as he picked up his hammer and saw!
I get what you are saying now Brad!
Q; why would tuning a Husky the way I have for all this time be fine, yet I have problems with my 7900's? Touchy carbs? hearing loss on my part?? :msp_confused:


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## Axlerod74 (Jan 18, 2012)

I am still trying to get a feel for this technique. Sorry, don't mean to take away from the OP.......:msp_rolleyes:

http://www.arboristsite.com/chainsaw/154314.htm


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## Mastermind (Jan 18, 2012)

Pics....


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## blsnelling (Jan 18, 2012)

Here's the vid I mentioned.

<iframe width="640" height="480" src="http://www.youtube.com/embed/5BZkB9QQTJU?rel=0" frameborder="0" allowfullscreen></iframe>


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## blsnelling (Jan 18, 2012)

Mastermind said:


> Pics....



I've got a hunch you've built a runner I like what I see!


----------



## parrisw (Jan 18, 2012)

cutmaster said:


> parrisw,
> I'll sell you one but I have to warn you; Dolmar 7900's will flip you right over the top of a large tree laying on the ground such as the tree in your pic, I've had such good luck with these bad boys using any other saw is like cutting trees with a hack saw! So get your wallet out!
> No really, I don't know what in the world is going on with all of mine, all of them are 2008 models.
> Don't know if that is my issue or what......
> By 2008 being an issue I am saying they had been sitting brand new in a warehouse for years, not that 2008 was a bad year...



I'll be ok. :msp_biggrin: PM sent.

Will


----------



## parrisw (Jan 18, 2012)

Randy. Looking good. Any numbers for us junky's.


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## deye223 (Jan 19, 2012)

blsnelling said:


> Here's the vid I mentioned.
> 
> gday brad was that a ported 460


----------



## Mastermind (Jan 19, 2012)

Numbers.....for the junkies. 

82 intake
98 exhaust
126 transfers

.030 popup
removed .010 from the squish band....

I'm putting it together now...


----------



## watsonr (Jan 19, 2012)

Randy,
Did you do anything to the upper transfers or the exhaust? Would like to see a picture if you did, I may have missed it?


----------



## Mastermind (Jan 19, 2012)

watsonr said:


> Randy,
> Did you do anything to the upper transfers or the exhaust? Would like to see a picture if you did, I may have missed it?



A lot has been done to both. I'm in the shop on my laptop now though and can't post pics.


----------



## srcarr52 (Jan 19, 2012)

Mastermind said:


> Numbers.....for the junkies.
> 
> 82 intake
> 98 exhaust
> ...



Or in durations... 

Intake 164
Exhaust 164
Transfers 108
Putting blowdown at 28 <- IMO thats a lot of blowdown. :msp_biggrin: Going for fuel economy? Or with the crankcase compression of the 7900 you just don't need that much transfer timing?

I also like keeping the intake:exhaust around 1:1, what goes in must come out.


----------



## blsnelling (Jan 19, 2012)

Sorry about going of topic here Randy. I'm anxious to see this baby run!


----------



## Mastermind (Jan 19, 2012)

srcarr52 said:


> Or in durations...
> 
> Intake 164
> Exhaust 164
> ...




Everyone says that the 7900 needs mucho blowdown. We shall see. 



blsnelling said:


> Sorry about going of topic here Randy. I'm anxious to see this baby run!



Oh heck, this thread has had some great info shared in it. Anytime I post a thread I only do it to share what I've learned........derailing is where the best stuff comes from sometimes.


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## blsnelling (Jan 19, 2012)

It surely does like lots of BD. You can make a great runner of other models with maybe half that amount.


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## srcarr52 (Jan 19, 2012)

Mastermind said:


> Everyone says that the 7900 needs mucho blowdown. We shall see.



I've also heard that they have a very small crankcase that gives them a lot of crankcase compression. You think this has something to do with not needing much transfer timing? :msp_confused: I see for once you've done extensive lower transfer work, thinking it already has enough transfer port velocity? oke:


----------



## Mastermind (Jan 19, 2012)

srcarr52 said:


> I've also heard that they have a very small crankcase that gives them a lot of crankcase compression. You think this has something to do with not needing much transfer timing? :msp_confused: *I see for once you've done extensive lower transfer work, thinking it already has enough transfer port velocity?* oke:




Exactly. The 7900 has a small crankcase, and the ring end makes it hard to widen the uppers enough. Plus if they aren't being raised too much there's not a lot of time/area there. I widened the entire transfer tract so I could open the exhaust side of them a bit without losing the angle of entry. 

This saw has more time in the port work than two normally do.


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## wendell (Jan 19, 2012)

Mastermind said:


> Pics....



Stop hijacking this thread! :msp_mad:


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## booger1286 (Jan 19, 2012)

Im excited to see. When is the video comin.


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## Mastermind (Jan 19, 2012)

wendell said:


> Stop hijacking this thread! :msp_mad:



If we ever get to meet Ima kick you in the pants. :hmm3grin2orange:


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## srcarr52 (Jan 19, 2012)

Mastermind said:


> Exactly. The 7900 has a small crankcase, and the ring end makes it hard to widen the uppers enough. Plus if they aren't being raised too much there's not a lot of time/area there. I widened the entire transfer tract so I could open the exhaust side of them a bit without losing the angle of entry.
> 
> This saw has more time in the port work than two normally do.



I do the same on 394's because of the locator pin location is already close to the intake side of the transfer ports and there is plenty of room left on the exhaust side to open it up without loosing the inlet angle.

Did you cut the squish band or use the sand paper mandrel trick?

I spent all last week making the fixtures to mount a cylinder in that lathe to cut squish bands but my first saw in that I was going to do it to (Stihl MS660) has a large ring of unplated cylinder. So I don't think I'll drop the cylinder much on this one, just a quick touch up with sand paper and 0.005" off the base. I’d rather it be a little lower on compression than I like then dropping the top ring into the ring of death. :msp_mad: I was really interested in see what they would do with less then stock exhaust timing since they are already at 167 stock.

Wait... :arg: Sorry Wendell.


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## Mastermind (Jan 19, 2012)

srcarr52 said:


> I do the same on 394's because of the locator pin location is already close to the intake side of the transfer ports and there is plenty of room left on the exhaust side to open it up without loosing the inlet angle.
> 
> Did you cut the squish band or use the sand paper mandrel trick?
> 
> ...




I just finished a 394. I used a 395 piston since the locator pins are both above the intake port. That way you can go wild on the uppers. 

The BB 064 I just built has much lower intake timing than stock. It turned out to have #### load of torque, but not so much rpm.....13,400 unloaded.


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## Metals406 (Jan 19, 2012)

Correct me if I'm wrong, but as a rule of thumb, is it?
↓
↓

The less crankcase volume, the more velocity in the trans, and they can benefit from a little area work on lowers and directing uppers.

Larger crankcase volume, lower trans velocity, benefit from less trans area work on the lowers to retain that needed velocity, but benefits from directing and smoothing/blending.


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## parrisw (Jan 19, 2012)

Metals406 said:


> Correct me if I'm wrong, but as a rule of thumb, is it?
> ↓
> ↓
> 
> ...



That's what I always thought Nate.


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## Mastermind (Jan 19, 2012)

Metals406 said:


> Correct me if I'm wrong, but as a rule of thumb, is it?
> ↓
> ↓
> 
> ...



Yep, that's what I think. The 7900 is known to have a very tight crankcase with a 79cc topend.

That's why I did so much transfer work on this saw.


----------



## Jon1212 (Jan 19, 2012)

Metals406 said:


> Correct me if I'm wrong, but *as a rule of thumb*, is it?
> ↓
> ↓
> 
> ...



Uh Oh, now this is gonna get personal. Please don't make "thumb" jokes in the presence of Randy. 


He is quite sensitive about his 3/4 digit, especially since the last time he hitchhiked the guy thought he only wanted a ride part way there.............LOL!!!!


----------



## Mastermind (Jan 19, 2012)

Jon1212 said:


> Uh Oh, now this is gonna get personal. Please don't make "thumb" jokes in the presence of Randy.
> 
> 
> He is quite sensitive about his 3/4 digit, especially since the last time he hitchhiked the guy thought he only wanted a ride part way there.............LOL!!!!



Your 261 is in a box.......not sure it'll ever get mailed now......:msp_confused:


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## Metals406 (Jan 19, 2012)

I hAz dAH Smartz in Mah brainz! 

:waaaht:


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## Jon1212 (Jan 19, 2012)

Mastermind said:


> Your 261 is in a box.......not sure it'll ever get mailed now......:msp_confused:



Well that's just plain dirty Randy. In fact, that is meanspirited as well. I was afraid this might happen spending all this time over here in the Chainsaw Forum with the likes of Brad.......LOL!!!
I was tryin' to bring the OT Forum to you, since you are obviously to busy to come visit us..........LOL!!!!


----------



## Mastermind (Jan 19, 2012)

Jon1212 said:


> Well that's just plain dirty Randy. In fact, that is meanspirited as well. I was afraid this might happen spending all this time over here in the Chainsaw Forum with the likes of Brad.......LOL!!!
> I was tryin' to bring the OT Forum to you, since you are obviously to busy to come visit us..........LOL!!!!



I'm sorry and stuff. 

Some rep might being me back to my senses......I ain't gettin any.


----------



## o8f150 (Jan 19, 2012)

Mastermind said:


> Your 261 is in a box.......not sure it'll ever get mailed now......:msp_confused:



:hmm3grin2orange::hmm3grin2orange::hmm3grin2orange:


----------



## o8f150 (Jan 19, 2012)

Mastermind said:


> I'm sorry and stuff. ...I ain't gettin any.



so your not getting any???? just come up to paducah and you can get it for 5.00 a pop:msp_biggrin::msp_biggrin:


----------



## Metals406 (Jan 19, 2012)

Mastermind said:


> I'm sorry and stuff.
> 
> Some rep might being me back to my senses......I ain't gettin any.



Gotcha some rep. . . Found it in the corner. :msp_biggrin:


----------



## Jon1212 (Jan 19, 2012)

Mastermind said:


> I'm sorry and stuff.
> 
> Some rep might being me back to my senses......I ain't gettin any.



Just further proof that your OT Bro's and Ho's care way more than these Chainsaw Cranks.:msp_sad:


----------



## 8433jeff (Jan 19, 2012)

I think the next "Mastermoob meets blah blah" should be in the off topic side.

Always off the track anyways, and it would be easier to explain to people that we're about saws and stuff, and stuff.


----------



## srcarr52 (Jan 19, 2012)

Mastermind said:


> I just finished a 394. I used a 395 piston since the locator pins are both above the intake port. That way you can go wild on the uppers.
> 
> The BB 064 I just built has much lower intake timing than stock. It turned out to have #### load of torque, but not so much rpm.....13,400 unloaded.



I thought about relocating the pins but you can get enough flow without doing it. I've found they too like a lot of intake timing... around 158 as apposed to the stock 140, widen out the transfers and they get by with more then stock blowdown 20 as apposed to stock 16. It does help them sip as apposed to guzzle fuel. 

I can't remember exactly but I thought the 395 pistons have a little less skirt on them so I couldn't go as far on the exhaust and intake width. Hopefully I'll find the bits and pieces to put together my last 394/395 carcase, this time I want to try a 395BB kit but I need the missing intake/carb setup. 

I think the low unloaded RPM is pretty typical for BB kits. You're probably better off that way as well since there is a little more mass going up and down. I'm always trying to lighten pistons on ported saws to help them from tearing themselves to bits. Back in day our racing program found out that our piston failures (pin pulling out the bottom) was due to the mass of the piston bending the piston transverse to the pin boss and causing the pin to crack out the bottom of the piston. The solution was to go to non full skirt pistons (very closely resembling the one you just put in this Dolmar) that also had webs between the pin bosses. Haven't had a problem since with our Dirt Late Model 870hp turning 9200RPM, 418ci SB2 motors, but we spent a lot of money figuring out all problems.


----------



## srcarr52 (Jan 19, 2012)

8433jeff said:


> I think the next "Mastermoob meets blah blah" sound be in the off topic side.
> 
> Always off the track anyways, and it would be easier to explain to people that we're about saws and stuff, and stuff.



Dislike! :msp_biggrin:


----------



## Mastermind (Jan 19, 2012)

I've moved on to the next saw. The Dolmar is running great. :msp_thumbup:

Them mufflers are a ##### though. :hmm3grin2orange:


More pics and video later. :msp_thumbsup:


----------



## parrisw (Jan 19, 2012)

There ya go teasing us again!

Ya mufflers are a biatch! I took mine apart and gutted it.


----------



## bryanr2 (Jan 19, 2012)

Mastermind said:


> I've moved on to the next saw. The Dolmar is running great. :msp_thumbup:
> 
> Them mufflers are a ##### though. :hmm3grin2orange:
> 
> ...



That video can't get here soon enough. Been glued to this thread.


----------



## Mastermind (Jan 19, 2012)

Pics.....

I'll get the video uploaded when I get through working for the night.


----------



## wendell (Jan 19, 2012)

Mastermind said:


> If we ever get to meet Ima kick you in the pants. :hmm3grin2orange:



I'm sure you'll find some excuse not to show up again since you're already 0 for 2.


----------



## Mastermind (Jan 19, 2012)

wendell said:


> I'm sure you'll find some excuse not to show up again since you're already 0 for 2.



West KY this spring if I'm alive, I'll be there. You bring that junky old 346xp and I'll bring my wildthing.


----------



## 8433jeff (Jan 19, 2012)

wendell said:


> I'm sure you'll find some excuse not to show up again since you're already 0 for 2.



Easy, big fella. Them saws you just bought need modding, too.


----------



## wendell (Jan 19, 2012)

Mastermind said:


> West KY this spring if I'm alive, I'll be there. You bring that junky old 346xp and I'll bring my wildthing.



I've been your way twice. Time for you to head north of the Mason Dixon.


----------



## Mastermind (Jan 19, 2012)

North? Why???? :hmm3grin2orange:


----------



## Mastermind (Jan 19, 2012)

I'm working on a Husqvarna 455 Rancher.......the smell in the shop is overwhelming me..... :mad2:


----------



## blsnelling (Jan 19, 2012)

Shut up and post a video already!!!!!!!!!!!!!!!!!


----------



## Mastermind (Jan 19, 2012)

blsnelling said:


> Shut up and post a video already!!!!!!!!!!!!!!!!!



Grinding some chains then I'm done....


----------



## mweba (Jan 19, 2012)

Mastermind said:


> Grinding some chains then I'm done....



Chains chains chains.....its gots powa right? Who needs a sharp chain?







Sorry, just prepping you for the drive by "your chain looks dull" comment on the tube.


----------



## blsnelling (Jan 19, 2012)

He's probably got the chain on the saw backwards stoning the cutters right now


----------



## tlandrum (Jan 19, 2012)

really brad ,i dont think randy gets stoned nowadays:hmm3grin2orange:


----------



## mweba (Jan 19, 2012)

Don't know....heard through the grape vine his favorite movie is clockwork orange:hmm3grin2orange:


----------



## Hedgerow (Jan 19, 2012)

mweba said:


> Don't know....heard through the grape vine his favorite movie is clockwork orange:hmm3grin2orange:



UH-OH... That's bad...:eek2:


----------



## booger1286 (Jan 19, 2012)

too bad you cant sell tickets to this looks like everybody is waitin on the video


----------



## blsnelling (Jan 19, 2012)

booger1286 said:


> too bad you cant sell tickets to this looks like everybody is waitin on the video



I think the crowd has him skeerd:hmm3grin2orange:


----------



## Mastermind (Jan 19, 2012)

The videos are uploading. 

The first cut was really light handed, then I added a bit more force each cut. It's pulling an 8pin and that chain ain't been sharpened in some time......

The second video is after a bit of tuning. It seems to be pretty strong but what do I know?


----------



## blsnelling (Jan 19, 2012)

The chain ain't sharp? Whatcha been doin all nite?


----------



## Mastermind (Jan 19, 2012)

blsnelling said:


> I think the crowd has him skeerd:hmm3grin2orange:




I wouldn't bet on that if I was you. :hmm3grin2orange:


----------



## Mastermind (Jan 19, 2012)

blsnelling said:


> The chain ain't sharp? Whatcha been doin all nite?



Welp it ain't dull either. :msp_thumbup:


----------



## NORMZILLA44 (Jan 19, 2012)

This thread grew quick my friend, popular saw?? LOL! Hey popular builder too


----------



## o8f150 (Jan 19, 2012)

Mastermind said:


> It seems to be pretty strong but what do I know?



not a damn thing:biggrin::hmm3grin2orange::biggrin::hmm3grin2orange:


----------



## Mastermind (Jan 19, 2012)




----------



## o8f150 (Jan 19, 2012)




----------



## booger1286 (Jan 19, 2012)

Sounds great and looks to be very strong.


----------



## booger1286 (Jan 19, 2012)

What type of wood is that?


----------



## Mastermind (Jan 19, 2012)

o8f150 said:


>



Yeah, but what do you know????


----------



## Mastermind (Jan 19, 2012)

booger1286 said:


> What type of wood is that?



It's just pine.


----------



## o8f150 (Jan 19, 2012)

Mastermind said:


> Yeah, but what do you know????



:cry3::cry3::cry3: going to tell my mommy:biggrin::biggrin:


----------



## Hedgerow (Jan 19, 2012)

79 cc's of Dolmar awesomeness.... Just don't blow it up while yer messin with it there monkey man...


----------



## blsnelling (Jan 19, 2012)

What kind of RPMs is it holding in the cut with a moderate load? How's the throttle response off idle?


----------



## booger1286 (Jan 19, 2012)

You should get you a big piece of locust, that stuff is like cuttin on a rock. I like the way you break em in. Just build em and bury em.


----------



## mt.stalker (Jan 19, 2012)

SMOKIN !!! enjoy some rep


----------



## booger1286 (Jan 19, 2012)

blsnelling said:


> What kind of RPMs is it holding in the cut with a moderate load? How's the throttle response off idle?



What helps give you the quick throttle response when portin a saw.


----------



## o8f150 (Jan 19, 2012)

booger1286 said:


> Just build em and bury em.



thats what echos are for:biggrin:


----------



## Hedgerow (Jan 19, 2012)

booger1286 said:


> You should get you a big piece of locust, that stuff is like cuttin on a rock. I like the way you break em in. Just build em and bury em.



And here I thought Locust was soft wood ... :msp_confused:


----------



## Mastermind (Jan 19, 2012)

Hedgerow said:


> 79 cc's of Dolmar awesomeness.... Just don't blow it up while yer messin with it there monkey man...



I'll try not too. I'm leaving it a little fat. Them unlimited coils scare me and stuff. :msp_ohmy:



blsnelling said:


> What kind of RPMs is it holding in the cut with a moderate load? How's the throttle response off idle?



I don't know what rpm it will hold. Too many variables to that equation. It's got very good throttle response, Jon did some limbing and bucking with it before it got dark. He really likes it. 



booger1286 said:


> What helps give you the quick throttle response when portin a saw.



More flow I reckon....


----------



## nmurph (Jan 19, 2012)

booger1286 said:


> What helps give you the quick throttle response when portin a saw.



A quick finger, the same thing that helps in a lot of situations.


----------



## Metals406 (Jan 19, 2012)

So Stumpy ported this saw?? :biggrin:


Randy, she hold really good rpm brother.


----------



## Mastermind (Jan 19, 2012)

Metals406 said:


> So Stumpy ported this saw?? :biggrin:
> 
> 
> Randy, she hold really good rpm brother.



I was impressed with it, considering it's wearing an 8pin it is pulling well. :msp_thumbup:


----------



## Jacob J. (Jan 19, 2012)

nmurph said:


> A quick finger, the same thing that helps in a lot of situations.



Like when I break through the toilet paper...


----------



## WKEND LUMBERJAK (Jan 19, 2012)

That is a nice running saw. The chain looked like it was throwing nice chips to.


----------



## Hedgerow (Jan 19, 2012)

WKEND LUMBERJAK said:


> That is a nice running saw. The chain looked like it was throwing nice chips to.



Yep, good build Randy... :msp_thumbup:


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## mt.stalker (Jan 19, 2012)

nmurph said:


> A quick finger, the same thing that helps in a lot of situations.



A quick finger helped me become a cunning linguist :hmm3grin2orange:


----------



## Andyshine77 (Jan 20, 2012)

Randy she sounds really good and it has snappy throttle response, I think you did an excellent job.


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## booger1286 (Jan 20, 2012)

Hedgerow said:


> And here I thought Locust was soft wood ... :msp_confused:



Poplar and pine is soft to me. Locust is a very dense dry wood,thats why everyone makes posts out of em here because they last in the ground and weather. Dont know, is oak like pine to you too?


----------



## booger1286 (Jan 20, 2012)

nmurph said:


> A quick finger, the same thing that helps in a lot of situations.



Its good everyone has fun here but is there not anyone that has enough knowledge of PORTING to tell me what kind of changes in port timing gives you the quicker throttle response? Its obvious quicker flow in and out of cylinder is a big help, but besides flow and widening ports such as timing , duration and crankcase pressure? It looks to me like higher crankcase pressures would be a big factor?


----------



## parrisw (Jan 20, 2012)

booger1286 said:


> Its good everyone has fun here but is there not anyone that has enough knowledge of PORTING to tell me what kind of changes in port timing gives you the quicker throttle response? Its obvious quicker flow in and out of cylinder is a big help, but besides flow and widening ports such as timing , duration and crankcase pressure? It looks to me like higher crankcase pressures would be a big factor?



By just widening the ports you'll see a big increase in throttle response.


----------



## Mastermind (Jan 20, 2012)

Andyshine77 said:


> Randy she sounds really good and it has snappy throttle response, I think you did an excellent job.



Thanks Andre, I can count on you to tell it like it. I'll admit to being very careful and doing a ton of reading for this saw. The 7900 is a saw that I've heard can go the wrong way. 



booger1286 said:


> Poplar and pine is soft to me. Locust is a very dense dry wood,thats why everyone makes posts out of em here because they last in the ground and weather. Dont know, is oak like pine to you too?



Locust is a dense wood, and it lasts forever for fence posts. When I moved here 26 years ago there were locust posts that were in the ground since the late '70s. Those posts are still there holding a fence. 

The reason pine was used in that video is because that's what I had at the time. I did some comparison cuts with 372s and needed a clear, consistent wood to make my results meaningful. I downed a whole tree to get the cant I used so for the next couple of weeks all my testing will be done in pine. 

If you look through my utube channel you will see videos in all sorts of wood. I just use what I have available at the time. One thing I've noticed in testing these saws is that soft wood will pull the rpm down on a saw because of chip loading, just because a wood is relatively soft doesn't always make for a fast cut.


----------



## o8f150 (Jan 20, 2012)

Mastermind said:


> Locust is a dense wood, and it lasts forever for fence posts. When I moved here 26 years ago there were locust posts that were in the ground since the late '70s. Those posts are still there holding a fence.
> 
> The reason pine was used in that video is because that's what I had at the time. I did some comparison cuts with 372s and needed a clear, consistent wood to make my results meaningful. I downed a whole tree to get the cant I used so for the next couple of weeks all my testing will be done in pine.
> 
> If you look through my utube channel you will see videos in all sorts of wood. I just use what I have available at the time. One thing I've noticed in testing these saws is that soft wood will pull the rpm down on a saw because of chip loading, just because a wood is relatively soft doesn't always make for a fast cut.



dang,, i just learned something


----------



## parrisw (Jan 20, 2012)

Mastermind said:


> If you look through my utube channel you will see videos in all sorts of wood. I just use what I have available at the time. One thing I've noticed in testing these saws is that soft wood will pull the rpm down on a saw because of chip loading, just because a wood is relatively soft doesn't always make for a fast cut.



Well said Randy. I've been trying to say that for years, some people never get it though.


----------



## srcarr52 (Jan 20, 2012)

booger1286 said:


> Its good everyone has fun here but is there not anyone that has enough knowledge of PORTING to tell me what kind of changes in port timing gives you the quicker throttle response? Its obvious quicker flow in and out of cylinder is a big help, but besides flow and widening ports such as timing , duration and crankcase pressure? It looks to me like higher crankcase pressures would be a big factor?



Better balance from intake to exhaust flow with help with throttle response but it's more a function of just generally flow through the whole engine. When you have higher peak flow generally the flow will be able to accelerate quicker giving you better throttle response. So when the saw is at idle, the flow through the engine is say 10% of when it's at 10,000 RPM. The faster you can go from idle flow to peak flow the more throttle response you'll have. 

Also anything you do to lighten the rotating assembly will help once you have the port flow.


----------



## Mastermind (Jan 20, 2012)

srcarr52 said:


> Better balance from intake to exhaust flow with help with throttle response but it's more a function of just generally flow through the whole engine. When you have higher peak flow generally the flow will be able to accelerate quicker giving you better throttle response. So when the saw is at idle, the flow through the engine is say 10% of when it's at 10,000 RPM. The faster you can go from idle flow to peak flow the more throttle response you'll have.
> 
> Also anything you do to lighten the rotating assembly will help once you have the port flow.



Thanks for giving him a good answer. I was tired last night and couldn't really think of a good way to put it. 

One reason I think this saw runs as well as it seems to is the new style, light weight piston that was used. I have another 7900 on my bench for port work with a windowed piston. I'll be contacting the owner about changing that.


----------



## Metals406 (Jan 20, 2012)

Another consideration for "softwoods" is where they grew. High elevation pine, fir, spruce, white fir, etc will be harder than pine grown in the south.

Why? Tighter growth rings and tougher wood fibers. It get's cold here, with lots of snow and wind. These trees don't have the growth rate of southern woods where it can stay 50° or better all winter. Northern climates also don't have as long a growing season,giving trees less time between sap up, and sap down. 

I've cut Doug Fir with growth rings averaging 1/16" or less apart. . . Some of them 1/32" apart for a 25 year stretch at a time.

There's a reason studs coming out of tree farms aren't as structurally strong as out of State forests, where they had to compete for water, sun, nutrients, battle wind and snow. . . It makes tougher wood.


----------



## srcarr52 (Jan 20, 2012)

Mastermind said:


> Thanks for giving him a good answer. I was tired last night and couldn't really think of a good way to put it.
> 
> One reason I think this saw runs as well as it seems to is the new style, light weight piston that was used. I have another 7900 on my bench for port work with a windowed piston. I'll be contacting the owner about changing that.



I do like the design of that piston... it's strong, light, and most likely allows more flow to the transfers then a ported piston. The only downside is without the flow through the piston the underside of the dome is not being cooled as much. So they must be banking on the pin boss wings to act as cooling fins for the piston dome. If you start seeing carbon build up (or massive discoloration) on the bottom of the piston dome then you know you got problems.


----------



## nmurph (Jan 20, 2012)

Metals406 said:


> Another consideration for "softwoods" is where they grew. High elevation pine, fir, spruce, white fir, etc will be harder than pine grown in the south.



Maybe, but a 30" pine in this part of the state will have heartwood for 2/3 of the diameter. That heart wood is packed full of hard sap and is like cutting through bubble gum. If you pick up a piece of what we call "fat" wood and a piece of oak the same size, the fat wood is noticeably heavier. That also depends greatly on the species. Loblolly, and Slash to a lesser extent, are softer until they get to the 25-30"+ size. Now, anything up to about 20" is pretty soft.


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## blsnelling (Jan 20, 2012)

Have you compared it to the 460 you did for the build off? How'd it fair against the 372s?


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## booger1286 (Jan 20, 2012)

Was not criticizing for using pine just thought it would be interesting to see a comparison between that and something like locust, because i just cut some the other day and it was just so much slower than red oak cutting.


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## steve316 (Jan 20, 2012)

*wrist pin*

Randy the only 7900 cylinder I have looked at is the new style. My question is dose the old style also have the tapered pin; as it is lighter than the 6400 witch is a standard pin.I read a post that the new piston was 12 grams lighter and was thinking ( this causes most of my problems ) the pin might be part of the weigh savings.Steve


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## Hedgerow (Jan 20, 2012)

srcarr52 said:


> Better balance from intake to exhaust flow with help with throttle response but it's more a function of just generally flow through the whole engine. When you have higher peak flow generally the flow will be able to accelerate quicker giving you better throttle response. So when the saw is at idle, the flow through the engine is say 10% of when it's at 10,000 RPM. The faster you can go from idle flow to peak flow the more throttle response you'll have.
> 
> Also anything you do to lighten the rotating assembly will help once you have the port flow.



What effect would advancing the timing a couple degrees have on throttle response?


----------



## HEAVY FUEL (Jan 20, 2012)

Metals406 said:


> Another consideration for "softwoods" is where they grew. High elevation pine, fir, spruce, white fir, etc will be harder than pine grown in the south.
> 
> Why? Tighter growth rings and tougher wood fibers. It get's cold here, with lots of snow and wind. These trees don't have the growth rate of southern woods where it can stay 50° or better all winter. Northern climates also don't have as long a growing season,giving trees less time between sap up, and sap down.
> 
> ...



We've used some fresh cut cottonwood for gtg racing 24-26 inches, your lucky to get thru it without pinching or plugging up with chips.


----------



## blsnelling (Jan 20, 2012)

Hedgerow said:


> What effect would advancing the timing a couple degrees have on throttle response?



On some saws, it has a huge affect on throttle response. It's a big part of the fix on the new 201T.


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## Hedgerow (Jan 20, 2012)

HEAVY FUEL said:


> We've used some fresh cut cottonwood for gtg racing 24-26 inches, your lucky to get thru it without pinching or plugging up with chips.



That's why I like the harder stuff for comparison cutting... You take the chain's ability to clear things out, "out" of the equation... I wonder if this is why race chain shines in competition cutting?? :msp_confused:
Slice and clear as fast as the saw can move it???


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## Hedgerow (Jan 20, 2012)

blsnelling said:


> On some saws, it has a huge affect on throttle response. It's a big part of the fix on the new 201T.



Just wonderin'... Seemed to help the old 028 a little, but I've convinced myself of things that aren't necessarily so before... 
:confident:


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## Mastermind (Jan 20, 2012)

Hedgerow said:


> What effect would advancing the timing a couple degrees have on throttle response?



I won't advance ignition timing on a worksaw. I worry about the added heat, especially when I'm adding compression.

The beveled wrist pin is part of the weight savings and is different than the windowed piston.


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## srcarr52 (Jan 20, 2012)

Hedgerow said:


> What effect would advancing the timing a couple degrees have on throttle response?



It can help. But only if the saw needs more then a few degrees of timing for max power. Most saws are fixed timing so at lower RPM they are wasting some of the cylinder pressure while the piston is still coming up in the bore from too much ignition timing. Since the time in seconds till peak pressure (dwell) in the cylinder is roughly the same for all RPM of the engine a fixed timing will only produce the maximum output from the combustion in a short RPM band, the rest of the RPM band is a compromise. 

Advancing the timing usually increase the throttle response because we are using better (higher octane) fuels then what the engine was originally designed for. The higher octane causes slower combustion dwell time and the more ignition timing needed to absorb the most of the combustion process. Think of cylinder pressure as a function of time after ignition so you have to place that spark at the appropriate time such that the most of the pressure is caught while the piston rod has good leverage on the crank pin. The leverage of the piston rod assembly is a function of angle of the crank. So our cylinder pressure is time dependent, our leverage is angle dependent, if our ignition timing is fixed the two equations can only be maximize for one point in the RPM band. Which is fine because we uses saws at a small RPM range when in the cut anyway.


----------



## blsnelling (Jan 20, 2012)

In using pump gas and find significant improvements in both throttle response and power under load. Not all saws respond the same though. It's just another part of tuning a saw, similar to tuning a carb. It's just more difficult to adjust.


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## Jon1212 (Jan 20, 2012)

Jon1212 said:


> Well that's just plain dirty Randy. In fact, that is meanspirited as well. I was afraid this might happen spending all this time over here in the Chainsaw Forum with the likes of Brad.......LOL!!!
> I was tryin' to bring the OT Forum to you, since you are obviously to busy to come visit us..........LOL!!!!





Mastermind said:


> I'm sorry and stuff.
> 
> Some rep might being me back to my senses......I ain't gettin any.



Well since you seem sincere, and because you're a good friend, I sent you some rep. Now ship me my dern saw.


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## Mastermind (Jan 20, 2012)

Jon1212 said:


> Well since you seem sincere, and because you're a good friend, I sent you some rep. Now ship me my dern saw.



:hmm3grin2orange:

It's going out in the morning. I think it's my best 261/262 yet. Enjoy it my friend. I'll always remember the generosity you showed me when I was sick and broke. You are the one that's a good friend.


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## bryanr2 (Jan 20, 2012)

This may be hijacking Randy, but I think I know ya well enough to get away with it...... Have you ever ported any other two cycle other than saws? I read a writeup where Brad ported a new Shindaiwa Blower and had "mad success" with it. I think after you get done with all my saws (and I have a few more to go) that I might have you do a little work on my Stihl FS 250R weedeater. It's the biggest and baddest line trimmer you can buy. I think I payed north of $500 for it a few summers ago. It's mean as it is, but if there are gains to be made.... I want them. I know it aint a chainsaw but I can put blades on it and cut saplings so hope this post dont get me in trouble. What do ya think?


----------



## FSburt (Jan 20, 2012)

Hey bryan I have a stihl weedeater and I ported the muffler and its a badass trimmer now. Mows down stuff that it used to bog down in before.


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## Mastermind (Jan 20, 2012)

bryanr2 said:


> This may be hijacking Randy, but I think I know ya well enough to get away with it...... Have you ever ported any other two cycle other than saws? I read a writeup where Brad ported a new Shindaiwa Blower and had "mad success" with it. I think after you get done with all my saws (and I have a few more to go) that I might have you do a little work on my Stihl FS 250R weedeater. It's the biggest and baddest line trimmer you can buy. I think I payed north of $500 for it a few summers ago. It's mean as it is, but if there are gains to be made.... I want them. I know it aint a chainsaw but I can put blades on it and cut saplings so hope this post dont get me in trouble. What do ya think?



I've even built weedwackers with popup pistons. I practiced on lots of stuff. :hmm3grin2orange:


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## bryanr2 (Jan 20, 2012)

Done the muffler- i want what's next. Agree though- totally different.


----------



## booger1286 (Jan 20, 2012)

bryanr2 said:


> This may be hijacking Randy, but I think I know ya well enough to get away with it...... Have you ever ported any other two cycle other than saws? I read a writeup where Brad ported a new Shindaiwa Blower and had "mad success" with it. I think after you get done with all my saws (and I have a few more to go) that I might have you do a little work on my Stihl FS 250R weedeater. It's the biggest and baddest line trimmer you can buy. I think I payed north of $500 for it a few summers ago. It's mean as it is, but if there are gains to be made.... I want them. I know it aint a chainsaw but I can put blades on it and cut saplings so hope this post dont get me in trouble. What do ya think?



I have a fs 80 that i ported, set the squish, muffler modded, and put new rings in and it has plenty of power. you cant keep it from twisting in your hand when you throttle up quick. I would like to get a steel shaft out of a fs 85 to put in it im afraid the cable will break.


----------



## bryanr2 (Jan 20, 2012)

So you have done one or two? The 'want' may become 'necessity' bout the time spring gets here and it's time to cut Grannie's and my Mom and Dad's yard this year. I've got commercial mowers and can mow my Grannie's property in 45 min but it takes 2.5 to 3 hrs to trim. She's one of those gals that plants stuff wherever there is a bare spot. Massive amounts of trimming.


----------



## bryanr2 (Jan 20, 2012)

booger1286 said:


> I have a fs 80 that i ported, set the squish, muffler modded, and put new rings in and it has plenty of power. you cant keep it from twisting in your hand when you throttle up quick. I would like to get a steel shaft out of a fs 85 to put in it im afraid the cable will break.



That's the performance I want!!!!!!!! And the fs250 already has the steel shaft. It's a "over kill" machine.


----------



## wendell (Jan 20, 2012)

bryanr2 said:


> That's the performance I want!!!!!!!!



Take a deep breath there, Sparky. You're scaring the children. :msp_scared:


----------



## naturelover (Jan 20, 2012)

I would really like to see some magic work on the FS-250!!! 

Not that I would do that to mine, its got plenty of power.

Dang thing is rough on plants and flowers sometimes...


----------



## Andyshine77 (Jan 20, 2012)

Mastermind said:


> Thanks Andre, I can count on you to tell it like it. I'll admit to being very careful and doing a ton of reading for this saw. The 7900 is a saw that I've heard can go the wrong way.



Any time my man. I hear if you put 372 like numbers in a 7900 you'll have yourself a really nice, super awesome looking boat anchor.:msp_sleep:


----------



## bryanr2 (Jan 20, 2012)

wendell said:


> Take a deep breath there, Sparky. You're scaring the children. :msp_scared:



My children are in bed!- FINALLY. lol


----------



## bryanr2 (Jan 20, 2012)

naturelover said:


> I would really like to see some magic work on the FS-250!!!
> 
> Not that I would do that to mine, its got plenty of power.
> 
> Dang thing is rough on plants and flowers sometimes...



Me too! Randy can we get a thread on this if I send it with a brush blade? The 250 is one mean machine stock- cant imagine what it would be ported.


----------



## Mastermind (Jan 20, 2012)

bryanr2 said:


> Me too! Randy can we get a thread on this if I send it with a brush blade? The 250 is one mean machine stock- cant imagine what it would be ported.



I'd be glad to port it for you Steven. The thread would have to go in another area of the site though. The saw nuts would lynch us for posting it here.


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## bryanr2 (Jan 20, 2012)

Mastermind said:


> I'd be glad to port it for you Steven. The thread would have to go in another area of the site though. The saw nuts would lynch us for posting it here.



Not if the video shows it cutting down a small tree.:hmm3grin2orange:


----------



## Mastermind (Jan 20, 2012)

bryanr2 said:


> Not if the video shows it cutting down a small tree.:hmm3grin2orange:



Good point.......very good point.


----------



## bryanr2 (Jan 20, 2012)

And we already have interest from other members. I wanna see the build and I want to own the test subject. There are tons of threads that are not "chainsaw" threads on this part of the site. They are however "wood" related. If that thing cuts a small tree down (which it will) if should be A-OK.


----------



## Buffhunter (Jan 20, 2012)

I would love to see that chit that would be too awesome


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## Mastermind (Jan 20, 2012)

You fellers have talked me into it. Hope I don't get banned. :hmm3grin2orange:


----------



## bryanr2 (Jan 20, 2012)

Mastermind said:


> You fellers have talked me into it. Hope I don't get banned. :hmm3grin2orange:



Ahh, you've passed the "trial period" you're a "lifer" now. It will be an educational thread on porting from the mastermind!


----------



## bryanr2 (Jan 21, 2012)

I've created a Sig. Posting to see if it works.


----------



## booger1286 (Jan 21, 2012)

Mastermind said:


> You fellers have talked me into it. Hope I don't get banned. :hmm3grin2orange:



I cant wait to see this.


----------



## bryanr2 (Jan 21, 2012)

Me too man. Might have to bump this build up in front of a few of my saws.


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## cutmaster (Jan 21, 2012)

Dolmar 7900's to brush cutter modds this thread is getting better all the time!
I got me an FS75 meself, I'd like it hopped up too but I don't use it much anymore since I bought the Scag ZTR - wife says " what did you do to my flowers? " I say oh crap! I thought them was weeds! :eek2:
It's too much fun cutting everything with this thing I figure why get off and get the trimmer out!:cool2:


----------



## bryanr2 (Jan 21, 2012)

cutmaster said:


> Dolmar 7900's to brush cutter modds this thread is getting better all the time!
> I got me an FS75 meself, I'd like it hopped up too but I don't use it much anymore since I bought the Scag ZTR - wife says " what did you do to my flowers? " I say oh crap! I thought them was weeds! :eek2:
> It's too much fun cutting everything with this thing I figure why get off and get the trimmer out!:cool2:



been there done that! i dont use a weedeater on my place either. I just let the goats have at it. but i do have a need for it on grannies, and mom and dads property


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## Mastermind (Jan 22, 2012)

Dolmar 7900 with a windowed piston. Same numbers as the other saw. I did file the chain though. 

[video=youtube;WyFQBUgLAx4]http://www.youtube.com/watch?v=WyFQBUgLAx4&list=UUg2yelCeKwB12xIohZfmf1g&index=1&feature=plcp[/video]


----------



## o8f150 (Jan 22, 2012)

Mastermind said:


> Dolmar 7900 with a windowed piston. Same numbers as the other saw. I did file the chain though.
> 
> [video=youtube;WyFQBUgLAx4]http://www.youtube.com/watch?v=WyFQBUgLAx4&list=UUg2yelCeKwB12xIohZfmf1g&index=1&feature=plcp[/video]


----------



## bryanr2 (Jan 22, 2012)

Mastermind said:


> Dolmar 7900 with a windowed piston. Same numbers as the other saw. I did file the chain though.
> 
> [video=youtube;WyFQBUgLAx4]http://www.youtube.com/watch?v=WyFQBUgLAx4&list=UUg2yelCeKwB12xIohZfmf1g&index=1&feature=plcp[/video]



I got the Makita version 64cc and the 7900 pc and hd filter in a box (waiting for install). gives me something to look forward too. Sucker was screaming!


----------



## komatsuvarna (Jan 22, 2012)

I see one of these in Randys future.........



Looks good man. Kinda makes me want one!


----------



## Mastermind (Jan 22, 2012)

komatsuvarna said:


> I see one of these in Randys future.........
> 
> 
> 
> Looks good man. Kinda makes me want one!



I gots a 6401 on the shelf. 

They are light as hell and when modded.........well.


----------



## bryanr2 (Jan 22, 2012)

komatsuvarna said:


> i see one of these in randys future.........
> 
> :d
> 
> looks good man. Kinda makes me want one!




everyone should have one!


----------



## Hedgerow (Jan 22, 2012)

komatsuvarna said:


> I see one of these in Randys future.........
> 
> 
> 
> Looks good man. Kinda makes me want one!



Oh, you know you want one... 
Mmmm Hmmmm.....
An stuff...


----------



## Stumpys Customs (Jan 22, 2012)

I should have my own 6401 makita before too long


----------



## bryanr2 (Jan 22, 2012)

Stumpys Customs said:


> I should have my own 6401 makita before too long



I kinda like the blue version expecially when you put the black dolmar cover and HD filter kit on it. Looks badazz. Hey Stumpy- theres a thread going (i think it is entitled Husky blue cover) and we were talking about paint and all. I mentioned your stumpbroke 372 that you painted all black (hammer finish). Can you post a picture of it in that thread? Thanks


----------



## Stumpys Customs (Jan 22, 2012)

bryanr2 said:


> I kinda like the blue version expecially when you put the black dolmar cover and HD filter kit on it. Looks badazz. Hey Stumpy- theres a thread going (i think it is entitled Husky blue cover) and we were talking about paint and all. I mentioned your stumpbroke 372 that you painted all black (hammer finish). Can you post a picture of it in that thread? Thanks



I'll do that.


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## NORMZILLA44 (Jan 22, 2012)

Sweet Randy:monkey:


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## bryanr2 (Jan 22, 2012)

Stumpys Customs said:


> I'll do that.



Thanks Stumpy.:msp_thumbup:


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## Jwalker1911 (Jan 22, 2012)

That saw runs like a top im saving my pennies for a ported saw in my future


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## wendell (Jan 22, 2012)

komatsuvarna said:


> Looks good man. Kinda makes me want one!



I thought you had decided that last fall. :msp_ohmy:


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## timmcat (Jan 22, 2012)

Pretty f'in strong runner. Is that cherry your cutting?


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## bryanr2 (Jan 22, 2012)

timmcat said:


> Pretty f'in strong runner. Is that cherry your cutting?


 
believe i read in the thread it was pine- but i read so much i might be wrong.


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## bryanr2 (Jan 22, 2012)

Jwalker1911 said:


> That saw runs like a top im saving my pennies for a ported saw in my future



That's the smartest thing you've said all day my man!:hmm3grin2orange::msp_thumbup:


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## Stumpys Customs (Jan 23, 2012)

Jwalker1911 said:


> That saw runs like a top im saving my pennies for a ported saw in my future



I like that idea:msp_thumbsup:


----------



## Andyshine77 (Jan 23, 2012)

Randy it looks strong, but I think the first saw sounds like it has a a bit more snap. What do you think??


----------



## Jwalker1911 (Jan 23, 2012)

bryanr2 said:


> That's the smartest thing you've said all day my man!:hmm3grin2orange::msp_thumbup:



Youre the first person thats accused me of being smart since i joined!


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## Mastermind (Jan 23, 2012)

Andyshine77 said:


> Randy it looks strong, but I think the first saw sounds like it has a a bit more snap. What do you think??



I concur. Though this one surprised me with the amount of snot it slings. :msp_wink:

I did a bit more lower transfer work on this one hoping to negate the loss of the slab sided piston.


----------



## steve316 (Jan 23, 2012)

*dyno testing*

Randy, wouldn't it be nice to dyno both saws and compair the grafts of the power ban to each other to see what where they were different. It would be just another piece of the puzzle.You could even do a-b-a test.outstanding work by the way Steve


----------



## Mastermind (Jan 23, 2012)

I would love to build a dyno. I've been looking at using an alternator and stuff............


I'm too busy to pursue it though.


----------



## blsnelling (Jan 23, 2012)

Mastermind said:


> I did some comparison cuts with 372s and needed a clear, consistent wood to make my results meaningful.





blsnelling said:


> Have you compared it to the 460 you did for the build off? How'd it fair against the 372s?


What were the results of the 372 and 460 comparison?



Mastermind said:


> Dolmar 7900 with a windowed piston. Same numbers as the other saw. I did file the chain though.





Mastermind said:


> I concur. Though this one surprised me with the amount of snot it slings. :msp_wink:


I agree that this one looks stronger.


----------



## Mastermind (Jan 23, 2012)

blsnelling said:


> What were the results of the 372 and 460 comparison?




In a 10" cant the 372s were both the same no matter how the lowers were done. The one with unraised cylinder walls made more rpm. In no way did these results help me learn anything though. I didn't have any large wood nor the time to really do the testing justice. 





blsnelling said:


> I agree that this one looks stronger.



Which one? The first or second?


----------



## blsnelling (Jan 23, 2012)

Mastermind said:


> In a 10" cant the 372s were both the same no matter how the lowers were done. The one with unraised cylinder walls made more rpm. In no way did these results help me learn anything though. I didn't have any large wood nor the time to really do the testing justice.
> 
> 
> 
> ...


What I meant was, how do the 372s and 460 compare to these 7900s?

The 2nd one looks stronger.


----------



## Mastermind (Jan 23, 2012)

blsnelling said:


> What I meant was, how do the 372s and 460 compare to these 7900s?
> 
> The 2nd one looks stronger.



Ah. I've not really compared. Someone should check out the videos.....hint hint. 

The 2nd one huh? I thought the first one was a tad stouter.


----------



## blsnelling (Jan 23, 2012)

Mastermind said:


> Ah. I've not really compared. Someone should check out the videos.....hint hint.
> 
> The 2nd one huh? I thought the first one was a tad stouter.


I don't have a good stop watch with me, but the windowed one appears to be faster, holding more RPMs in the cut.

I think your 372s and 460 would take the 7900s. But you don't have vids in the same wood.


----------



## nstueve (Jan 23, 2012)

Stumpys Customs said:


> I should have my own 6401 makita before too long



Are you planning on going with a 79 or 84 cc kit or just modding the 6401 to see what you get? either way I've been looking at doing either or! And this thread makes me want to tear into it! Just wondering what your plans are!?!?!

nate


----------



## bryanr2 (Jan 23, 2012)

Mastermind said:


> Ah. I've not really compared. Someone should check out the videos.....hint hint.
> 
> The 2nd one huh? I thought the first one was a tad stouter.



Somebody else can check out the videos. Everytime I watch a video I go on the look out for a new saw. VIDEOS are not my friend!


----------



## bryanr2 (Jan 23, 2012)

blsnelling said:


> I don't have a good stop watch with me, but the windowed one appears to be faster, holding more RPMs in the cut.
> 
> I think your 372s and 460 would take the 7900s. But you don't have vids in the same wood.



agree with brad. ive watched and rewatched and i think the 2nd looks faster by a hair.


----------



## komatsuvarna (Jan 23, 2012)

bryanr2 said:


> agree with brad. ive watched and rewatched and i think the 2nd looks faster by a hair.



I think so too, but I think Randy said he sharpened the chain. I think the first one was a little more ''peppier''.


----------



## blsnelling (Jan 23, 2012)

The first didn't hold near the RPMs in the cut. I would go with windows and not raise the lowers so much. I'd also try more intake duration. I'm just thinking out loud, as I don't have these figured out either.


----------



## Saw Dr. (Jan 23, 2012)

naturelover said:


> I would really like to see some magic work on the FS-250!!!
> 
> Not that I would do that to mine, its got plenty of power.
> 
> Dang thing is rough on plants and flowers sometimes...



And stucco. Glad it was not in a conspicuous place on the side of the house where I started in with my "new" 250. That thing sounds like a dirt-bike. I love it. It is kinda tough to run at a very light throttle, though. I find mine 4-strokes heavily just off idle.


----------



## bryanr2 (Jan 23, 2012)

Saw Dr. said:


> And stucco. Glad it was not in a conspicuous place on the side of the house where I started in with my "new" 250. That thing sounds like a dirt-bike. I love it. It is kinda tough to run at a very light throttle, though. I find mine 4-strokes heavily just off idle.



Randy, I think we have another vote for a Stihl fs250 build.


----------



## Stumpys Customs (Jan 23, 2012)

nstueve said:


> Are you planning on going with a 79 or 84 cc kit or just modding the 6401 to see what you get? either way I've been looking at doing either or! And this thread makes me want to tear into it! Just wondering what your plans are!?!?!
> 
> nate



Gonna see what I can do with the 64cc top end first.


----------



## cbrduckdog (Jan 23, 2012)

bigredd said:


> That is definately the 7900 I sold to a fellow AS Member. Very interested in seeing how it turns out.



Ding, Ding, Ding Bigred you are correct.

Randy, looks like a fine saw, can't wait to run the beast. I have a special patch of woods on my farm for this saw.:msp_biggrin:


----------



## Andyshine77 (Jan 23, 2012)

blsnelling said:


> The first didn't hold near the RPMs in the cut.



Brad as you know things aren't always what they seem in videos, maybe he was pushing harder because of the chain, or whatever. My point is, it's pointless to really judge a saws power or rpm's without a tach, timed cuts and equal chains, or actually being there and running the saw IMHO. That's why I asked Randy.:msp_smile:


----------



## blsnelling (Jan 23, 2012)

Andyshine77 said:


> Brad as you know things aren't always what thy seem in videos, maybe he was pushing harder because of the chain, or whatever. My point is, it's pointless to really judge a saws power or rpm's without a tach, timed cuts and equal chains, or actually being there and running the saw IMHO. That's why I asked Randy.:msp_smile:



My comments were based on RPMs held in the cut by the same operator and timed cuts in the vids.


----------



## Andyshine77 (Jan 23, 2012)

blsnelling said:


> My comments were based on RPMs held in the cut by the same operator and timed cuts in the vids.



Did he give us a number from a tach? Sure we can go by sound, but sound isn't fact, especially sound from a video. Not trying to say you're wrong, but it's also not fact.:msp_smile:


----------



## Jon1212 (Jan 23, 2012)

In before closed


----------



## blsnelling (Jan 23, 2012)

OK, I take back my comment. I listened to these earlier on my phone. I just listened to them again and can't make the same comment:bang:


----------



## blsnelling (Jan 23, 2012)

Here they are together. Someone time them



Mastermind said:


> [video=youtube;C7O0RQ0BxWY]http://www.youtube.com/watch?v=C7O0RQ0BxWY[/video]
> 
> [video=youtube;V9skmQuOPpM]http://www.youtube.com/watch?v=V9skmQuOPpM[/video]





Mastermind said:


> Dolmar 7900 with a windowed piston. Same numbers as the other saw. I did file the chain though.
> 
> [video=youtube;WyFQBUgLAx4]http://www.youtube.com/watch?v=WyFQBUgLAx4&list=UUg2yelCeKwB12xIohZfmf1g&index=1&feature=plcp[/video]


----------



## Hedgerow (Jan 23, 2012)

blsnelling said:


> OK, I take back my comment. I listened to these earlier on my phone. I just listened to them again and can't make the same comment:bang:



Just use my favorite excuse... "STUPID PHONE!!!"
:ah:


----------



## Andyshine77 (Jan 23, 2012)

blsnelling said:


> There is no mistaking the difference in RPMs in those two vids. Don't need a tach to hear that



Well I must need a tach:msp_wink: because I don't hear much difference lol. This is the first video of Randy's 7900 build, to me it Sounds the best.

Edit Brad posts too fast.

<iframe width="420" height="315" src="http://www.youtube.com/embed/C7O0RQ0BxWY" frameborder="0" allowfullscreen></iframe>


----------



## Hedgerow (Jan 23, 2012)

All went so damn close to 3.3 seconds per cut it's scary...


----------



## Andyshine77 (Jan 23, 2012)

Brad just say it, come on now you can do it, repeat after me. I got owned!!!!:jester:


----------



## bryanr2 (Jan 23, 2012)

Hey Mastermind..... I'm calling you out! I was just wiping down all my saws and I got cheated out of a sticker on my Dolly 120si!:msp_sneaky: Dont let me forget it when I come to pick up the 044 and blower.
steven


----------



## blsnelling (Jan 23, 2012)

Andyshine77 said:


> Well I must need a tach:msp_wink: because I don't hear much difference lol. This is the first video of Randy's 7900 build, to me it Sounds the best.
> 
> Edit Brad posts too fast.
> 
> <iframe width="420" height="315" src="http://www.youtube.com/embed/C7O0RQ0BxWY" frameborder="0" allowfullscreen></iframe>



You caught me before I edited my post, lol. 

I just went back and timed them. The windowed piston saw is faster

*Non-Windowed*
4.20
3.58
3.46
3.61
3.63
*3.47*

*Windowed Piston*
3.57
*3.29*
3.32
3.31


----------



## Hedgerow (Jan 23, 2012)

Andyshine77 said:


> Well I must need a tach:msp_wink: because I don't hear much difference lol. This is the first video of Randy's 7900 build, to me it Sounds the best.
> 
> Edit Brad posts too fast.
> 
> <iframe width="420" height="315" src="http://www.youtube.com/embed/C7O0RQ0BxWY" frameborder="0" allowfullscreen></iframe>



7900's are just freaks... 
And stuff...


----------



## bryanr2 (Jan 23, 2012)

blsnelling said:


> here they are together. Someone time them



he's baiting us! (I cant afford another saw)


----------



## Hedgerow (Jan 23, 2012)

blsnelling said:


> You caught me before I edited my post, lol.
> 
> I just went back and timed them. The windowed piston saw is faster
> 
> ...



1st cut must be thrown out, two knots............
Also... Did Randy say he touched up the chain in the 2nd set of vids?


----------



## bryanr2 (Jan 23, 2012)

Hedgerow said:


> 1st cut must be thrown out, two knots............
> Also... Did Randy say he touched up the chain in the 2nd set of vids?



No but he said that the chain in the first one had not been sharpened in some time and that with the first video each cut he leaned on it progresssively harder.


----------



## bryanr2 (Jan 23, 2012)

Post # 150 of this thread (by Mastermind)

The videos are uploading. 

The first cut was really light handed, then I added a bit more force each cut. It's pulling an 8pin and that chain ain't been sharpened in some time......

The second video is after a bit of tuning. It seems to be pretty strong but what do I know?


----------



## blsnelling (Jan 23, 2012)

Andyshine77 said:


> Brad just say it, come on now you can do it, repeat after me. I got owned!!!!:jester:



Noooooooooooooo!!!!!!!!!!!!!!!!!! Better check my last post, lol:msp_biggrin:


----------



## bryanr2 (Jan 23, 2012)

blsnelling said:


> Noooooooooooooo!!!!!!!!!!!!!!!!!! Better check my last post, lol:msp_biggrin:



Brad- we just got better ears! I thought the 2nd was clearly the more aggressive.


----------



## blsnelling (Jan 23, 2012)

bryanr2 said:


> Brad- we just got better ears! I thought the 2nd was clearly the more aggressive.



I think that's what it is. Andre must have a cold and his ears are plugged up:jester:


----------



## Andyshine77 (Jan 23, 2012)

blsnelling said:


> I think that's what it is. Andre must have a cold and his ears are plugged up:jester:



My ears work just fine thank you lol. The numbers however are what they are.


----------



## Hedgerow (Jan 23, 2012)

bryanr2 said:


> Brad- we just got better ears! I thought the 2nd was clearly the more aggressive.



I think Randy started on the big end of the log, and it's getting smaller as he cuts on it...
:big_smile:


----------



## blsnelling (Jan 23, 2012)

Andyshine77 said:


> My ears work just fine thank you lol. The numbers however are what they are.



Are we actually talking on the phone and posting with each other at the same time?:biggrin:


----------



## bryanr2 (Jan 23, 2012)

Hedgerow said:


> 1st cut must be thrown out, two knots............
> Also... Did Randy say he touched up the chain in the 2nd set of vids?



I went back and looked and.....
You are correct- Randy did touch up the chain for the windowed piston saw.


----------



## Hedgerow (Jan 23, 2012)

bryanr2 said:


> I went back and looked and.....
> You are correct- Randy did touch up the chain for the windowed piston saw.



And I've come up with only one way to find out for sure... Randy must send both to me for testing... 
Then I will send them back along with my findings, covered in yellow sawdust...:msp_sneaky:


----------



## komatsuvarna (Jan 23, 2012)

Hedgerow said:


> And I've come up with only one way to find out for sure... Randy must send both to me for testing...
> Then I will send them back along with my findings, covered in yellow sawdust...:msp_sneaky:



NO!!! My 372 was sneezing yellow stuff for weeks!



:hmm3grin2orange::hmm3grin2orange:


----------



## Hedgerow (Jan 23, 2012)

komatsuvarna said:


> NO!!! My 372 was sneezing yellow stuff for weeks!
> 
> 
> 
> :hmm3grin2orange::hmm3grin2orange:



Awe c'mon Durand.... It's just dust!!! It makes saws last longer I hear...:msp_sneaky:


----------



## Hedgerow (Jan 23, 2012)

Come to think about it... I've been sneezing it for a while too...


----------



## Mastermind (Jan 23, 2012)

blsnelling said:


> You caught me before I edited my post, lol.
> 
> I just went back and timed them. The windowed piston saw is faster
> 
> ...





Hedgerow said:


> I think Randy started on the big end of the log, and it's getting smaller as he cuts on it...
> :big_smile:




Yep that's right. The non-windowed saw is cutting slightly larger wood AND I touched up the chain before I cut with the windowed saw.

I think they are both great runners.


----------



## Hedgerow (Jan 23, 2012)

Mastermind said:


> Yep that's right. The non-windowed saw is cutting slightly larger wood AND I touched up the chain before I cut with the windowed saw.
> 
> I think they are both great runners.



Bam!!! The real test offer still stands though...
Ya know... An stuff...


----------



## Mastermind (Jan 23, 2012)

Hedgerow said:


> Bam!!! The real test offer still stands though...
> Ya know... An stuff...



One is gone home and the other soon will.


----------



## NORMZILLA44 (Jan 23, 2012)

Good job Randy! I got a question of all the saws you have ever built, which one responded to improvements the most, any one model stand out?


----------



## Mastermind (Jan 23, 2012)

NORMZILLA44 said:


> Good job Randy! I got a question of all the saws you have ever built, which one responded to improvements the most, any one model stand out?



That's an easy one Norm. The Husqvarna 359 takes to mods like a Labrador Retriever takes to water.


----------



## unatool (Jan 23, 2012)

Yes, 359!

Like a tree climber to the top... heads-up!

P.S. - running the heck out of my snelling 201t... nice


----------



## NORMZILLA44 (Jan 23, 2012)

Nice, never would have guessed that.


----------



## Jon1212 (Jan 24, 2012)

NORMZILLA44 said:


> Good job Randy! I got a question of all the saws you have ever built, which one responded to improvements the most, any one model stand out?





Mastermind said:


> That's an easy one Norm. The Husqvarna 359 takes to mods like a Labrador Retriever takes to water.





NORMZILLA44 said:


> Nice, never would have guessed that.



Norm,
Randy is unintentionally blocking out my MS 390 that he opened up, and it is a night and day difference in that saw. I'm pretty sure Randy is just afraid to mention it because of the 25 pages of crap out of the 28 pages that thread generated...............LOL!!!!!


----------



## Andyshine77 (Jan 24, 2012)

NORMZILLA44 said:


> Nice, never would have guessed that.



Back in the day's when Ed/EHP was a member here the 359 were all the rage, a fire wood cutters dream, they'd out cut stock 372's 440's in 20" wood all day long.


----------



## steve316 (Jan 24, 2012)

*compression*

Randy;Did you check the compression before and after,mine is stock and on my gage it is 181psi. I had my gage calibrated so I feel this is half way correct and wondering what type of gain one could exspect with a pop-up plus .010 off the chamber.thanks for putting a great post. Steve


----------



## Mastermind (Jan 24, 2012)

Andyshine77 said:


> Back in the day's when Ed/EHP was a member here the 359 were all the rage, a fire wood cutters dream, they'd out cut stock 372's 440's in 20" wood all day long.



Ed was a big help in this 7900 build. 



steve316 said:


> Randy;Did you check the compression before and after,mine is stock and on my gage it is 181psi. I had my gage calibrated so I feel this is half way correct and wondering what type of gain one could exspect with a pop-up plus .010 off the chamber.thanks for putting a great post. Steve



I doubt I raised the compression much after raising the exhaust port. 

I'll check specter's saw tomorrow, Brian's is gone....


----------



## Andyshine77 (Jan 25, 2012)

Mastermind said:


> Ed was a big help in this 7900 build.
> 
> 
> 
> ...



Ed's helped me out many, many times, he's a standup guy in my book.


----------



## bcorradi (Jan 25, 2012)

It looks like you have a good runner....however I think a reallly good built 372 or 440 will beat it.


----------



## Mastermind (Jan 25, 2012)

Andyshine77 said:


> Ed's helped me out many, many times, he's a standup guy in my book.




Yes he sure seems to be. He always gives me a good clear answers when asked. I would say he's forgotten more about building two strokes than I may ever learn.



bcorradi said:


> It looks like you have a good runner....however I think a reallly good built 372 or 440 will beat it.



In this size and type of wood it's a close race for all these saws. I enjoy running a 7900 as they do seem light and handle well. I don't like the ass backward kill switch though.


----------



## Jwalker1911 (Jan 25, 2012)

Looks to me like you build a heck of a saw


----------



## Mastermind (Jan 25, 2012)

Jwalker1911 said:


> Looks to me like you build a heck of a saw



A lot of guys around here do. I just take my time and try hard to keep an open mind. I feel like forming concrete opinions about things stops our growth.....a new idea can't be grafted into a closed mind.


----------



## Andyshine77 (Jan 25, 2012)

Mastermind said:


> A lot of guys around here do. I just take my time and try hard to keep an open mind. I feel like forming concrete opinions about things stops our growth.....a new idea can't be grafted into a closed mind.



I couldn't have said it better myself. If you stick to one way and only one way, you never learn anything new.


----------



## Jon1212 (Jan 25, 2012)

Mastermind said:


> A lot of guys around here do. I just take my time and try hard to keep an open mind. I feel like forming concrete opinions about things stops our growth.....a new idea can't be grafted into a closed mind.





Andyshine77 said:


> I couldn't have said it better myself. If you stick to one way and only one way, you never learn anything new.



And that Ladies& Gentlemen is exactly how I ended up with my ported, and modded MS 390 by Randy (Mastermind). I've used it before, and after in front of my oldest boy's FIL, and he thought it was a different saw..........LOL!!!!


----------



## bryanr2 (Jan 25, 2012)

Mastermind said:


> A lot of guys around here do. I just take my time and try hard to keep an open mind. I feel like forming concrete opinions about things stops our growth.....a new idea can't be grafted into a closed mind.




Nominated for quote of the year. Well said.


----------



## bryanr2 (Jan 25, 2012)

bcorradi said:


> It looks like you have a good runner....however I think a reallly good built 372 or 440 will beat it.



We will know soon enough. I've got a 044 10mm in Mastermind's shop as we speak. I cant tell ya if it's on the bench or the floor, dut I do know it's in the door.

stevn


----------



## cbrduckdog (Jan 25, 2012)

bryanr2 said:


> We will know soon enough. I've got a 044 10mm in Mastermind's shop as we speak. I cant tell ya if it's on the bench or the floor, dut I do know it's in the door.
> 
> stevn



We can play, I am just south of you in Loudon County and the 7900 is at the post office waiting for pick-up. Would love to see how it performs.


----------



## bryanr2 (Jan 25, 2012)

cbrduckdog said:


> We can play, I am just south of you in Loudon County and the 7900 is at the post office waiting for pick-up. Would love to see how it performs.



Sounds good. Ive got the 6401 sitting in the garage and the 7900 kit and HD kit sitting in the house. After running Randys 44/46- I cant wait to get mine back. Dont know if to do the Makita, 288, or 2095 next. prob the kita so I can get these boxes out of the house.

What part Loudon County are you- Im in West Knox (Walker Springs/ Cedar Bluff area).


----------



## cbrduckdog (Jun 30, 2013)

Old thread new info: I have cut a lot of wood with this saw which was ported by Randy. It has the slab piston in it. I have always run it with an 8 pin and 24 inch bar. I just like the feel of the 8 pin with the 24 inch, personal preference I guess. I tried it with a 32 inch bar with skip tooth Stihl RSC which put a huge smile on my face, held 11,000+rpms in the cut, I did change it to a 7 pin but should have seen what it would do with the 8 pin. Oh well something to try next time. 
Anyway Randy Thanks!  I have not done this saw justice in reporting how good a job you did. If I find another 7900 I know who has the recipe! One SOB of a saw! Oh how do I get a sticker?


----------



## 7sleeper (Jun 30, 2013)

Always good to get a long term feedback! Better than some short term enthusiasm!

Rep sent!

7


----------



## Mastermind (Jun 30, 2013)

I just need your address.......that reminds me...........I am almost out of stickers again. :msp_wink:

When you ran that thing at the GTG I was eating a hotdog.....I thought "what in the hell is turning that much RPM in the cut?".

Seeing that saw run that strong helped me make some decisions on other builds we have in the works...that's for sure. :msp_sneaky:


----------



## Mastermind (Jul 1, 2013)

Mastermind said:


> I just need your address.......that reminds me...........I am almost out of stickers again. :msp_wink:
> 
> When you ran that thing at the GTG I was eating a hotdog.....I thought "what in the hell is turning that much RPM in the cut?".
> 
> Seeing that saw run that strong helped me make some decisions on other builds we have in the works...that's for sure. :msp_sneaky:



I sure wish I had a newer video of that saw............ :msp_thumbup:


----------



## redoakneck (Jul 1, 2013)

How much improvement over stock????


----------



## Hedgerow (Jul 1, 2013)

redoakneck said:


> How much improvement over stock????



40% of course...


Maybe 50!!!

:msp_thumbsup:


----------



## cbrduckdog (Jul 1, 2013)

Mastermind said:


> I sure wish I had a newer video of that saw............ :msp_thumbup:



I will see if I can help with at video. Give me a couple of weeks its hot but I am also traveling with work. BTW I have a 32" bar on order.


----------



## cbrduckdog (Jul 1, 2013)

redoakneck said:


> How much improvement over stock????



Tough for me to answer this question. It has been over 4 years since I ran a stock 7900. Back then I compared the 7900 to a 460 but felt better mainly due to the anti vibe I guess. This one only had 140psi when I got it so it needed help in my opinion. I have never checked compression since the build but I guess I could.

Is it better than stock yes, how much better is hard to answer. If I wasn't milling my 660 would find a new home.


----------



## ptjeep (Jul 1, 2013)

This saw runs way better than a stock one. How much better, it made me consider selling my ported 660 to get one. Is that good enough?:hmm3grin2orange:


----------



## Mastermind (Jul 1, 2013)

ptjeep said:


> This saw runs way better than a stock one. How much better, it made me consider selling my ported 660 to get one. Is that good enough?:hmm3grin2orange:



Hell my 395 was looking over it's shoulder......I think it's a little scared. :cool2:


----------



## Hedgerow (Jul 1, 2013)

Mastermind said:


> Hell my 395 was looking over it's shoulder......I think it's a little scared. :cool2:



It's hard to top a good 79er...
:msp_wink:


----------



## Andyshine77 (Jul 2, 2013)

Hedgerow said:


> It's hard to top a good 79er...
> :msp_wink:



You've got that right!!!


----------



## SawTroll (Jul 2, 2013)

Andyshine77 said:


> If I recall correctly the Walbro HD 12 carb that came on the 372 will bolt right in as well, not sure about the venturi size though.





Terry Syd said:


> The Walbro is actually a bit smaller than the Zama. Walbro is 16.67mm and Zama is 17mm.
> 
> ......



A bit late - but the HD-12 is 17.46mm. 16.67 is the HD-6. 

Likely, all those carbs really are too small, but that's another discussion....


----------



## Mastermind (Jul 2, 2013)

Hedgerow said:


> It's hard to top a good 79er...
> :msp_wink:





Andyshine77 said:


> You've got that right!!!



I never really put much thought into these saws anymore......I've done quite a few....but it seems like they don't show up for port work like they did a few years ago. 

When Chuck fired that thing up and laid it to the wood.....to say my ears perked up would be a huge understatement.


----------



## Hedgerow (Jul 2, 2013)

Mastermind said:


> I never really put much thought into these saws anymore......I've done quite a few....but it seems like they don't show up for port work like they did a few years ago.
> 
> When Chuck fired that thing up and laid it to the wood.....to say my ears perked up would be a huge understatement.



I still have one that's bone stock.. 
It's a fantastic saw in stock form...
Since its an every day user, it would cause me great pain to be without it for a month... 
I'm probably not alone.


----------



## Mastermind (Jul 2, 2013)

Hedgerow said:


> I still have one that's bone stock..
> It's a fantastic saw in stock form...
> Since its an every day user, it would cause me great pain to be without it for a month...
> I'm probably not alone.



When I get back I'll only be a week behind or so. I've stop talking work so I could get caught back up to a reasonable amount.


----------



## Andyshine77 (Jul 3, 2013)

Mastermind said:


> I never really put much thought into these saws anymore......I've done quite a few....but it seems like they don't show up for port work like they did a few years ago.
> 
> When Chuck fired that thing up and laid it to the wood.....to say my ears perked up would be a huge understatement.



I think the 7910 is likely the cause. I know you ported a 7910, how did it run compared to the older 7900's?

I have a barely used stock 7900 as well, they run so good stock it's hard to breakdown and take the time to port it. The one I have has 190+psi of compression and squish set at .018 out of the box, what's not to like.


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## Hedgerow (Jul 3, 2013)

Andyshine77 said:


> I think the 7910 is likely the cause. I know you ported a 7910, how did it run compared to the older 7900's?
> 
> I have a barely used stock 7900 as well, they run so good stock it's hard to breakdown and take the time to port it. The one I have has 190+psi of compression and squish set at .018 out of the box, what's not to like.





Nothing...
Saw nirvana...
:msp_wink:


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## Mastermind (Jul 3, 2013)

Andyshine77 said:


> I think the 7910 is likely the cause. I know you ported a 7910, how did it run compared to the older 7900's?
> 
> I have a barely used stock 7900 as well, they run so good stock it's hard to breakdown and take the time to port it. The one I have has 190+psi of compression and squish set at .018 out of the box, what's not to like.



I've done three 7910s in the last few months. I use the same numbers in them as the 7900.....but to be completely honest I can't say how they compare. I don't have enough trigger time on either to be a good one to ask. :msp_unsure:


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## Mastermind (Jul 31, 2013)

bcorradi said:


> I'm curious to see how it works out for you. All of the good builders that I know say they can get more out of a 440 and a 372 than they can out of a 7900.



I'm building two 7900s today......thought I'd look at this thread again.

This 7900 that was the object of this thread holds more rpm in the cut than any 372 or 440 that I've ever built. With a 28" 8 pin it was holding 11,400......


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## Metals406 (Jul 31, 2013)

It would take some serious pencil time -- but I wouldn't mind seeing the ratio of port/trans area to crankcase volume and combustion chamber volume/shape between the 372 and 7900.

Might be telling why it's more beastly.


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## Hedgerow (Jul 31, 2013)

Metals406 said:


> It would take some serious pencil time -- but I wouldn't mind seeing the ratio of port/trans area to crankcase volume and combustion chamber volume/shape between the 372 and 7900.
> 
> Might be telling why it's more beastly.



The 372 should have a lot more crank case volume... 
Both pretty badass...
Both quad ports...
Similarities end at this point?


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## nmurph (Jul 31, 2013)

It might be the 8cc extra of the 7900:hmm3grin2orange::hmm3grin2orange::hmm3grin2orange:

I have an EC 7900 and a 460 from Randy. I am going to have to drag them out and drop them in the big oak chunck I have and see how they spin up.

Randy, I bought a Walbro for the saw. Do I just file away about half the key in the FW to advance the timing?


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## Mastermind (Jul 31, 2013)

nmurph said:


> It might be the 8cc extra of the 7900:hmm3grin2orange::hmm3grin2orange::hmm3grin2orange:
> 
> I have an EC 7900 and a 460 from Randy. I am going to have to drag them out and drop them in the big oak chunck I have and see how they spin up.
> 
> Randy, I bought a Walbro for the saw. Do I just file away about half the key in the FW to advance the timing?



Take .020 off the key. Then use a rope or stop to hold the engine while you clock the flywheel CCW against the cut edge of the key.....as you are holding the flywheel, snug the nut as tight as you can get it. Then rotate the engine CW to the stop to finish tightening the nut.


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## Andyshine77 (Jul 31, 2013)

No doubt the 7900's pull harder than the 372's where it counts.opcorn:


This one was ported by EHP.
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## cattoon (Aug 1, 2013)

*I love statistics*



Hedgerow said:


> 40% of course...
> 
> 
> Maybe 50!!!
> ...



73% of all statistics are made up on the spot.


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## Hedgerow (Aug 1, 2013)

cattoon said:


> 73% of all statistics are made up on the spot.



"But it was on the internet, so it must be true"

~Abraham Lincoln~


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## SawTroll (Aug 1, 2013)

Andyshine77 said:


> If I recall correctly the Walbro HD 12 carb that came on the 372 will bolt right in as well, not sure about the venturi size though.





Terry Syd said:


> The Walbro is actually a bit smaller than the Zama. Walbro is 16.67mm and Zama is 17mm.
> 
> I would prefer a straight bolt on mod, I'm not keen on cobbling up things up to get them to fit. However, it is just a firewood saw not a production saw, so if things rattle loose I can always walk back to the shed.



According to the Walbro part list, the HD-12 is 17.46mm, while the HD-6 is 16.67.


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## Trx250r180 (Aug 1, 2013)

now that you have raised the bar with the 7900 ,you will just have to start building stronger 372's and 440's opcorn:


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## Mastermind (Aug 1, 2013)

Trx250r180 said:


> now that you have raised the bar with the 7900 ,you will just have to start building stronger 372's and 440's opcorn:



Finger porting a 7900 right now..........


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## Adirondackstihl (Aug 1, 2013)

Mastermind said:


> Finger porting a 7900 right now..........



Smell your fingers...........:hmm3grin2orange:





















oop:


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## Hedgerow (Aug 1, 2013)

Mastermind said:


> Finger porting a 7900 right now..........



Never would have thought to do that...
But hey, why not???
You going with the stock carb? Or un-decided?


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## Mastermind (Aug 1, 2013)

Hedgerow said:


> Never would have thought to do that...
> But hey, why not???
> You going with the stock carb? Or un-decided?



372 carb


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## Hedgerow (Aug 1, 2013)

Mastermind said:


> 372 carb



Good call... Can't wait to see it run...


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## Mastermind (Aug 1, 2013)

Hedgerow said:


> Good call... Can't wait to see it run...



We're doing two.......this first one is being a complete pain in our asses. Jon's about ready to chunk it in the woods. 

He just tore it back down to check everything.......it appears that the intake boot isn't sealing at the carb base.


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## Metals406 (Aug 1, 2013)

Mastermind said:


> Finger porting a 7900 right now..........



Welcome my brother. . . You are now part of the Society of Finger-Porting Addicts. . . Resistance is futile.


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## Metals406 (Aug 1, 2013)

Mastermind said:


> We're doing two.......this first one is being a complete pain in our asses. Jon's about ready to chunk it in the woods.
> 
> He just tore it back down to check everything.......it appears that the intake boot isn't sealing at the carb base.



Duct tape? opcorn:


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## Mastermind (Aug 1, 2013)

Metals406 said:


> Duct tape? opcorn:



####ty design me thinks. :hmm3grin2orange:


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## ptjeep (Aug 1, 2013)

Mastermind said:


> Finger porting a 7900 right now..........



Uhhhhhhh............... We're gonna need some vids of that one!:msp_w00t:


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## Mastermind (Aug 1, 2013)

ptjeep said:


> Uhhhhhhh............... We're gonna need some vids of that one!:msp_w00t:



If it ain't a turd I'll have at Jer's GTG.


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## Hedgerow (Aug 1, 2013)

Mastermind said:


> We're doing two.......this first one is being a complete pain in our asses. Jon's about ready to chunk it in the woods.
> 
> He just tore it back down to check everything.......it appears that the intake boot isn't sealing at the carb base.



Poor Jon...
He needs a raise..


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## Mastermind (Aug 1, 2013)

Hedgerow said:


> Poor Jon...
> He needs a raise..



For sure. 



We're using a 372 intake on ours......


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## Jimmy in NC (Aug 1, 2013)

Mastermind said:


> We're doing two.......this first one is being a complete pain in our asses. Jon's about ready to chunk it in the woods.
> 
> He just tore it back down to check everything.......it appears that the intake boot isn't sealing at the carb base.



Tell Jon I feel his pain right now.. got a 372 that wants to fight me right now.


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## cgraham1 (Jun 27, 2014)

Mastermind said:


> I enjoy running a 7900 as they do seem light and handle well. I don't like the ass backward kill switch though.


I'm thinking about sending my Dolmar to Randy, thought I'd bring up an old thread. Anybody else have their 7900 Masterminded? I'd love to hear some feedback... the pics and videos are gone from this thread. 

The kill switch thing makes me laugh, you can just pop it out and flip it over and then it's the same as a Husky!


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## Mastermind (Jun 27, 2014)

I remember this saw very well. I was at Terry's last GTG.....eating a hot dog. I hear a saw fire up, and make a few cuts. I could tell it was turning incredible RPM in the cut......so I got my tach and checked it. Nearly 12,000 RPM in the cut !!!!! My 372XP was turning about 100 less RPM......and I thought it was pretty mean. 

I asked the guy......."who ported this saw?"

He said you did Randy.....about three years ago. 

Welp.......I dug thru my notes.....and that saw was the saw in this thread. 

It has a new OEM top end with the lightweight slab sided piston....nothing special in the port work. No carb work or anything. 

I have my notes on it.......and still do every 7900 the same way. I just cut the squish now instead of doing a popup piston.


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## Mastermind (Jun 27, 2014)

And here it is......


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## cgraham1 (Jun 27, 2014)

Looks like it runs pretty good! 

I'm sure this has been discussed before, but... How do these saws compare to other ported saws in the same class, like the 372 or the 460/046? Or the 064 since you're already doing one for me?


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## Mastermind (Jun 27, 2014)

They are probably the fastest saw in their size range......


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## nstueve (Jun 27, 2014)

Mastermind said:


> They are probably the fastest saw in their size range......


Damn strait! Stock out of the box these are potent saws. Ported they are even better, obviously!


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## cgraham1 (Jun 27, 2014)

nstueve said:


> Damn strait! Stock out of the box these are potent saws. Ported they are even better, obviously!


My 7900 has sure impressed me, I was just wondering how well they take to being ported. 

BTW, your Makita is on the way. Hopefully you get some use out of it.


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## Mastermind (Jun 27, 2014)

I have a 6401 hanging on the rack here.......someday I'll play with it.


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## Adirondackstihl (Jun 27, 2014)

Thawt U No Like The Udder Jermin Sawz?
Dis Mean U Due My 7900 ?


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## Mastermind (Jun 27, 2014)

I hate Zama carbs.......Dolmars are fine saws.....


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## RiverRat2 (Jun 27, 2014)

Mastermind said:


> I hate Zama carbs.......Dolmars are fine saws.....


yeah the Zama's pretty much suck


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## cgraham1 (Jun 27, 2014)

Mastermind said:


> I hate Zama carbs.......Dolmars are fine saws.....





RiverRat2 said:


> yeah they pretty much suck


I know I could search, but I'm gonna be lazy and just ask. So.... what's the deal with the Zama carbs? and can you swap them with some other carb without a bunch of custom fabrication? Thanks


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## Adirondackstihl (Jun 27, 2014)

Walbro


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## Mastermind (Jun 27, 2014)

The 7900 will accept a Walbro from a 372 with no mods needed I believe.


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## cgraham1 (Jun 27, 2014)

Mastermind said:


> The 7900 will accept a Walbro from a 372 with no mods needed I believe.


I happen to have some 372 parts...

And a 7900...


And an appointment with Mastermind... So, what am I missing?


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## Mastermind (Jun 27, 2014)

I'm working on fixing the pics in this thread....


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## fordf150 (Jun 27, 2014)

Someday my 7900 will make the trip. For now I'm happy with the way it runs stock.


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## bryanr2 (Jun 27, 2014)

Mastermind said:


> And here it is......





Good God Im gonna need to get another one. .
Got the wheels turning..... starting to think about that brand new 6400 Dex is offering.


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## bryanr2 (Jun 27, 2014)

Clint- they are the King of the 70cc range. At 79cc, Id have to group them in the 80cc range though- and I think they hold their own pretty well in that class too. Many have considered the 064 to have had the best power to weight ratio in the past, that was until the 7900 came out. It is the reigning "power to weight" king.


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## RiverRat2 (Jun 28, 2014)

cgraham1 said:


> I happen to have some 372 parts
> And a 7900...
> []
> And an appointment with Mastermind... So, what am I missing?


Time money and patience,,, oh and 7900 are great saws,,, Zama carbs are not the best



bryanr2 said:


> Clint- they are the King of the 70cc range. At 79cc, Id have to group them in the 80cc range though- and I think they hold their own pretty well in that class too. Many have considered the 064 to have had the best power to weight ratio in the past, that was until the 7900 came out. It is the reigning "power to weight" king.



Yes on all counts!!!


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## Jakers (Jun 28, 2014)

Would swapping the carbs out cure the hot start flooding issues? My 7300 is awful that way


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## Mastermind (Jun 28, 2014)

Good question. 

Lean issues are what I see mostly from the Zamas that I have issues with. Heck.....not all of them are any trouble either.


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## Terry Syd (Jun 28, 2014)

All the Zama carbs I've looked at all have the same jetting - two .25mm jets. The jets can be drilled and the flow increased considerably. When a Zama is used on a bigger engine, they need a lot more flow. I've also tried blocking the auxiliary jet on a Zama and just used a drilled idle jet and with a stronger metering spring it may turn out to be an even better approach.

I'm just starting on modding the HDs. They are a bit more difficult to mod as you have to pull the welsh plug and redrill the air bleed/transition holes (and drilling the body of the carb is permanent, you can't replace the jet like on the Zama if you go too far). Since the HD-12 seems to be a popular carb, it would be great to find out what size holes are used on the carb body, that way someone could drill their existing carb to the HD-12 specs. Although, the HD-12 was used on a 71cc engine, so even the HD-12 might benefit from a bit of tweaking to use on a 79cc engine.


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## Gravedigger (Jun 29, 2014)

Mastermind said:


> I'm working on fixing the pics in this thread....




THANKS


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## nstueve (Jun 29, 2014)

Terry Syd said:


> All the Zama carbs I've looked at all have the same jetting - two .25mm jets. The jets can be drilled and the flow increased considerably. When a Zama is used on a bigger engine, they need a lot more flow. I've also tried blocking the auxiliary jet on a Zama and just used a drilled idle jet and with a stronger metering spring it may turn out to be an even better approach.
> 
> I'm just starting on modding the HDs. They are a bit more difficult to mod as you have to pull the welsh plug and redrill the air bleed/transition holes (and drilling the body of the carb is permanent, you can't replace the jet like on the Zama if you go too far). Since the HD-12 seems to be a popular carb, it would be great to find out what size holes are used on the carb body, that way someone could drill their existing carb to the HD-12 specs. Although, the HD-12 was used on a 71cc engine, so even the HD-12 might benefit from a bit of tweaking to use on a 79cc engine.


Would seem like walbro probably has a spec sheet on each carb that would provide this info...???


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## psuiewalsh (Jun 29, 2014)

What about a 390 carb?


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## Mastermind (Jun 29, 2014)

Yeah Keith, the 390, or 395 carb will work. A 288 air filter elbow is needed to connect the HD filter....


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## dolmarfan (Jun 29, 2014)

I am a offtopic but here goes:
Tuning dolmar 5000 with a limited coil.Tuning to keep under the rev limiter(13500rpm) requires H screw 3,5-4 turn CCW and my tach is still reading 13200rpm.I dont think I have a leak.Is this ok?
Thanks!


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## Mastermind (Jun 29, 2014)

Probably........

Those small saws tune sorta weird. Less airflow means more turns out on the H screw. 

I would find the limiter........then lean it out a little more at a time, checking the tune in the cut. As you lift the pressure it should still burble a little. 

Without the rev limiter, that saw would likely still four stroke at 14,500 or so.


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## psuiewalsh (Jun 29, 2014)

Mastermind said:


> Yeah Keith, the 390, or 395 carb will work. A 288 air filter elbow is needed to connect the HD filter....


Good to know. I just put one together and had to dig the epoxy out of the H screw hole. I will test next week and see if it wants more fuel.


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## psuiewalsh (Jun 29, 2014)




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## cheeves (Jun 29, 2014)

bryanr2 said:


> Clint- they are the King of the 70cc range. At 79cc, Id have to group them in the 80cc range though- and I think they hold their own pretty well in that class too. Many have considered the 064 to have had the best power to weight ratio in the past, that was until the 7900 came out. It is the reigning "power to weight" king.


I've run a lot of big saws in my younger days, and my 79 is as good if not better than any of them!! Just awesome to use!! Sheer Joy!!!


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## cbrduckdog (Jul 18, 2014)

Update, I still have this saw in this tread. Its still doing very well pulling a 32" skip tooth chain right now. I need to get some video of it since its what 3 years old now or something.


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## Mastermind (Jul 18, 2014)

Hello stranger. 

Good to see you here.


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## cbrduckdog (Jul 18, 2014)

Yea been real busy first time back here in a while. Work has me all over the world and the US.


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## mdavlee (Jul 18, 2014)

Nice to see you pop in. You still got that 066 I sold you?


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## dugide (Jul 18, 2014)

psuiewalsh said:


> Good to know. I just put one together and had to dig the epoxy out of the H screw hole. I will test next week and see if it wants more fuel.


should pressure/vac check, sounds like an air leak. L/H should be 1 and 1/2 turns out.


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## Terry Syd (Jul 19, 2014)

Here's an option on a 7900 carb, check out post #66. - http://www.arboristsite.com/community/threads/dolmar-7900-carb-upgrade.229528/page-4


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## cbrduckdog (Jul 19, 2014)

mdavlee said:


> Nice to see you pop in. You still got that 066 I sold you?


 Well a someone ran it an offered a Sig 229 DAK and I could not refuse.


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## mdavlee (Jul 19, 2014)

cbrduckdog said:


> Well a someone ran it an offered a Sig 229 DAK and I could not refuse.



I would have kicked your tail if you didn't trade for that.


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## wde_1978 (Dec 4, 2014)

Mastermind said:


>



Nice ! 

Wish I had any kind of stronger wood to cut to properly check my PS7900 out.


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## Freakingstang (Dec 4, 2014)

Hey Randy, how do these 7900's compare to a good running 064 that you've done? Ever had them side by side?


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## Big wood1 (Jan 15, 2019)

Mastermind said:


> Here's a few pics of a build I'm working on.
> 
> This is a nice clean saw. It had a Chinese top end and only 140psi...
> 
> ...


Can you tell me where to get that piston please. Thank you


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## Adirondackstihl (Jan 15, 2019)

Big wood1 said:


> Can you tell me where to get that piston please. Thank you


7910 piston


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## Big wood1 (Jan 15, 2019)

Adirondackstihl said:


> 7910 piston


Thanks.


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## Adirondackstihl (Jan 15, 2019)

Big wood1 said:


> Thanks.


OEM is your only bet 
Well.....unless you do your homework


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## Big wood1 (Jan 15, 2019)

Adirondackstihl said:


> OEM is your only bet
> Well.....unless you do your homework


Ya I want to try the lightwheight on my 6401 7900 upgrade!


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## Adirondackstihl (Jan 15, 2019)

Big wood1 said:


> Ya I want to try the lightwheight on my 6401 7900 upgrade!


----------

