Dolmar 7900 Carb upgrade?

[Poleman]

Thats what I'm hoping for Terry....was dissapointed when I recieved the back order notice. Yep everyones got the bug!!!! Lol

Sorry all about the pictures all over the page....

 

[RyanTowry_81]

Slow taper idle screws on back order.... I wonder is someone else jumped the gun and picked up YOUR idle screws. LOL

Maybe a few people that are going to try these mods should send in their order for the screws as soon as possible. It would be nice to have the screw/s on hand before tweaking the carb.

It wasn't me but now I know those are a long lead item I might just order a couple now so I can get my name on the list. Hope to have my carb by the end of the week

 

[Terry Syd]

Rich, good write up, I think everyone can read that explanation with the pictures and figure it all out.

As long as you are on back order, you might tell them to add a couple of the springs - before they end up on back order!

EDIT: Rich, are these the washers you are using? - http://www.scalehardware.com/produc...-11/1-4-mm-machined-washer-brass-qty-25-p-252

 

[Poleman]

That's a good idea Terry! I will contact them and get those also.

Yes those are the washers I'm using....the ones you suggested and that you use/have!!

Rich

 

[fordf150]

I ordered the screws yesterday from my distributor. In about 6 months they will show up and I will be able to send Rich my carb for modifications. By then he should have it all figured out

 

[Poleman]

Oh.....don't say 6 months.... I needed them yesterday!!!!! Never heard that before have you??? Lol.

Yep. By that time I will be in mass production....anodized blue carb all polished up and shinny with a lightning bolt across it....chrome Hi & Low screws and also a chrome slow taper screw.....and find forget to get your custom braided fue!l line and impulse line with crime a & n fittings. No one will want to cover this all up behind an air cleaner!!!!! I' m thinking custom K&N's on a voleocity stack for a ram air effect.

 

[fordf150]

The press in 90 degree fuel fittings take 2 to 3 months to come everytime I order them so 6 months for these seems reasonable.

 

[Gravedigger]

Oh.....don't say 6 months.... I needed them yesterday!!!!! Never heard that before have you??? Lol.

Yep. By that time I will be in mass production....anodized blue carb all polished up and shinny with a lightning bolt across it....chrome Hi & Low screws and also a chrome slow taper screw.....and find forget to get your custom braided fue!l line and impulse line with crime a & n fittings. No one will want to cover this all up behind an air cleaner!!!!! I' m thinking custom K&N's on a voleocity stack for a ram air effect.

I'm in for the works once available

 

[Poleman]

AWSOME GRAVEDIGGER......YOU'LL have some major BLING going on that saw......then you can throw a BIG rooster tail at all your friends with chips from it!!!!! It will run as good as it looks!!!!!

 

[cgraham1]

3 weeks and my saw is headed to Mastermind.

I don't need all that bling. I just want my saw to run at it's maximum potential.

 

[Terry Syd]

You'll have to order the 'bare bones' model. No bling, looks like a stock carb - just install and go. It's made for commercial cutters that don't care what their equipment looks like, they just want it to WORK.

 

[RyanTowry_81]

Bare bones is good for the sleeper look too, especially with the 365 stickers still. Really surprise people what a "65cc" saw can do. Haha

 

[Terry Syd]

You should see what a Chinese 365, otherwise known as the 'HH365 Gasoline Chainsaw' can do to their facial expressions, - what a hoot!

I've heard through the grapevine that the chainsaw racers in Oz have created a separate class for the Poleman Carb, just like when they designated rotary valve kart engines to a separate class. Instead of 77cc Unlimited, the Poleman Carb has to run in the 77AA class.

 

[Poleman]

Well its looking like a second carb option will be needed......the sleeper!!!

I'm thinking distressed body, looking like its been cycled to long in an ultrasonic with to much heat and poor choice of solutions!!?? Then and metal parts will receive a rusting plate and chrome flecking. Lastly the carb will receive the leaky sawdust top coat making it look like its never been off the saw or a kit or maintaince EVER done to it!!!

Do you think this will fill the sleeper void??? Did I miss anything??

 

[Terry Syd]

Sounds like the carb on my saw, and I didn't pay extra for the 'look'. You may have a hard sell on that line of carbs.

 

[Poleman]

Lol.....but custom distressed!!!!!! For that barn find look. Look at the price women pay for a worn out pair of jeans...GOLDMINE!!!!! I understand guys are wired differently than women tho...

Just talking this through....most guys could do this themselves....ya, probably wouldn't have much demand...

Dreams dashed.......

 

[Terry Syd]

More ideas. nmurph and I got in a discussion about a C3M on a 346. As I recall the 346 has a 15mm carb. It should also have the same .25/.25 jet combination. I understand that the 346 is considered a good limber, but down on torque for the big stuff compared to some other 50cc saws.

OK, what if a .30/.25 would bring the torque back up. Especially if someone used a 17mm body for the carb where the velocity though the carb would be reduced. If we established a 50cc jetting and we already have a 80cc jetting, then we could roughly compute where a 65cc and 71cc engine would need to be jetted.

I'll try to put a rough guide together using the area of the jets. It is only a starting point, but at least it is a place to start.

 

[CR888]

Terry this is a great thread! l wonder what you could do to a Solo 681 carb (walbro) for improvments....this thread has got me thinking. l like how you approach a carb modd. There is certainly lots that can be tweaked before boring out venturis. Some OPE IMO never reaches its potential due to a compromised carb for epa or whatever reasons.

 

[Terry Syd]

I've got the old Walbro HD-5 that came on my 029 sleeper. It is an emissions carb with two jets, the low speed circuit is limited to ONE .25mm jet. Even a stock Zama is double that flow in the low speed circuit.

I'm still tweaking the Zama that I put on the 029 and I need to go back into the engine to increase the timing on the transfers, but when I've got it where I want it, I'm going to mod the Walbro to see if I can get it as good or better than the Zama.

I'll do a thread for the Walbro folks when I do.

 

[Poleman]

Well....worked on the Zama that will go to Randy today...little biwillfferent than the others. This had a double D Hi screw, than I noticed these carb had a hole drilled in the throttle plate. I measured it at .80mm.

Drilled the jets to 30/40, double checked needle height and tested this way. Started easily but was running rich and needed more air. It did have idle adjustment the way it was. I then opened up the throttle plate hole to .90mm and retested.....better. One more try this time to 1.00mm. This seemed to do the trick for adjustability and engine performance. The throttle was a little slow now so I tryed a shim and a spring change....nope not it. Left the shim and put original spring back in....that's more like it!!!!

The saw was still a little rich but I figure after Randy gets finished doing his port work on the 7900 it should be real close...or that's my intentions. This carb has a lot of top end to work with!!

Looking to make these as painless as possible to put on a saw and go!! Hopefully I will be getting some feedback soon as to how accurate settings are and power results.