Carb tuning/mods for modded saw?

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Rusty-880

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Have a ported 880 giving me trouble trying to figure out how to set the tune on it. Ports matched for 8,500rpm with extra transfer added feeding off intake (slotted from intake passage to same height as stock transfers, int exh porst are quite big compared to stock). At idle dosn't want to idle above 2000rpm with L screw at 1/2 turn, any further in it's too lean to run smooth. At this setting with H JUST off seat saw runs too rich when cutting. Apart from this saw has much broader power curve, if I get tune sorted should run better. I have heard that needle and seat spring tension can play a big part in tuning. Is there a way to set it from measuring pulse pressure from crankcase? Do you usualy need small mods to carb after decent port changing?
Carb is Tillotson.

Thanks, Steve
 
Rusty-880 said:
Have a ported 880 giving me trouble trying to figure out how to set the tune on it. Ports matched for 8,500rpm with extra transfer added feeding off intake (slotted from intake passage to same height as stock transfers, int exh porst are quite big compared to stock).
[snip]
Thanks, Steve
Click to expand...

That won't work on a piston ported engine. :(

If you had a reed engine you can do that, but in a piston ported engine there is no way to close the intake port with that mod when you are trying to push the charge up from the crankcase, all you'll achieve is to bleed off pressure and push the fresh charge from the crankcase out through the inlet port and carby.

You'll need a new cylinder and start from there.

If you want to try and add boost/finger ports, you need to feed them from the crankcase.
 
Not arguing just asking, wouldn't the piston skirt close the intake to the crankcase and the carb feed the transfer? Think I know what you mean, crankcase pressure goes into combustion chamber and out transfer to carb?
If thats the case I'm even more confused now because cranking pressure is 110psi, and with the right pressure on saw it cuts just as fast if not a touch more at 8-9000rpm on the mill but if chain gets clogged will keep cutting at 4-5000rpm to clear chain then pick up instead of stalling chain as it used to.
If I have mucked it up I'm thinking it could be easier to fit reed valve as new cyl is about $800 in aus. I have a spare cyl with a small gouge in crankcase chamber to use in mean time if I need to.
 
Rusty, pics will help alot. take some of what you have done. It my be able to be saved??? maybe not???? I have NO experience with STihl...but those settings on a husky would lean seize it in a heart beat.... But dont stress, youve probably learnt more in a month than most in a year ;)
 
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The port could be filled back in with GB Weld, or what I use in Oz is a Pertex liquid metal.

The port is not in a overly hot spot and would likely retain the filler. You can clean and rough up the port, lay some duct tape on the inside of the cylinder and pour in the filler. After it sets, pull off the tape, then turn the piston upside down and use the bottom of the piston skirt to 'bump' into any of the filler that might need triming off. If the skirt hits it, smooth it off. The piston ring will smooth off any that you didn't get.

Cheaper than a new jug.
 
Try and get some on tomorrow. Problem with learning now is I've been trying to start business doing slab furniture and have been working on getting mill a bit quicker so we don't spend as long cutting and more time making... :msp_biggrin: That and I can't leave well enough alone at the best of times:msp_tongue:
My cousin was slabbing today and says its fast with light feed pressure so wont swap cylinders tonight.
 
Rusty-880 said:
Try and get some on tomorrow. Problem with learning now is I've been trying to start business doing slab furniture and have been working on getting mill a bit quicker so we don't spend as long cutting and more time making... :msp_biggrin: That and I can't leave well enough alone at the best of times:msp_tongue:
My cousin was slabbing today and says its fast with light feed pressure so wont swap cylinders tonight.
Click to expand...

Sounds like you have killed a good cylinder! wanna slab quicker buy a lucas slabber, or build one.

I disagree with what terry has said there and permatex will not handle the temps required if it is where I understand it is. JB weld might, but I wouldn't guarantee it!


I would say Rick is on the money! new pot needed.
 
Rusty-880 said:
Not arguing just asking, wouldn't the piston skirt close the intake to the crankcase and the carb feed the transfer? Think I know what you mean, crankcase pressure goes into combustion chamber and out transfer to carb?
If thats the case I'm even more confused now because cranking pressure is 110psi, and with the right pressure on saw it cuts just as fast if not a touch more at 8-9000rpm on the mill but if chain gets clogged will keep cutting at 4-5000rpm to clear chain then pick up instead of stalling chain as it used to.
If I have mucked it up I'm thinking it could be easier to fit reed valve as new cyl is about $800 in aus. I have a spare cyl with a small gouge in crankcase chamber to use in mean time if I need to.
Click to expand...

110 PSI is way too low you should be 145 or better. Not sure what you mean by the gouge in the crankcase chamber of a cylinder, that just makes no sense! Actually the whole post I have quoted makes no sense!
 
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If the transfers close before exhaust would you lose that much more than what you lose out the exhaust? Slot is approx10mm 3/8" wide and about 3mm 1/8" deep in midpoint. Pics tomorrow
 
masculator said:
110 PSI is way too low you should be 145 or better. Not sure what you mean by the gouge in the crankcase chamber of a cylinder, that just makes no sense!
Click to expand...

Gouge- Damage. Make more sense?
How 145psi or better?? Took .032" off the spare cylinder, kept tripping decomp valve by half stroke on a pullstart and only gave 135psi. Stock MS361 gives 85psi
 
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I'll have to check tomorrow, but I believe it is an Italian 'Pertex' not 'Permatex' that is called 'Cold Weld'. It is rather expensive, but sets up well. It is suppose to be good for something like 800F and can be filed like metal after it sets. I've been surprised at the quality of the stuff and have started using it for all sorts of things just because I can count on it not letting go - bugger the expense.

I'll get the particulars tomorrow when I can get to the shed without getting soaked.
 
masculator said:
Sounds like you have killed a good cylinder! wanna slab quicker buy a lucas slabber, or build one.

I disagree with what terry has said there and permatex will not handle the temps required if it is where I understand it is. JB weld might, but I wouldn't guarantee it!


I would say Rick is on the money! new pot needed.
Click to expand...

I built this mill. Currently will do log 800-850mm wide 7m long. If I buy anything will be a bandsaw mill, if they'll handle the hardwood without too much extra cost. Can't have killed the cyl that much, wont stall the chain like it used to.
 
I picked up some JB Weld on Monday at Bursons, good for 310*C or so apparently.

I was looking for Devcon or similar at the engineering supplies and found the JB at the car parts place !
 
Rusty-880 said:
Gouge- Damage. Make more sense?
How 145psi or better?? Took .032" off the spare cylinder, kept tripping decomp valve by half stroke on a pullstart and only gave 135psi. Stock MS361 gives 85psi
Click to expand...

You make less sense with each post!!!

you should be getting a minimum of 145 psi on a worn out 088/ms 880. a stock ms 361 that gives 85 psi will not run and would be minimum 160 psi of compression!

Think you need to make more sense! how the fark do you get a gouge in the Crankcase chamber of a cylinder???? It makes no logical sense the cylinder does not have a crankcase chamber!
 
tdi-rick said:
I picked up some JB Weld on Monday at Bursons, good for 310*C or so apparently.

I was looking for Devcon or similar at the engineering supplies and found the JB at the car parts place !
Click to expand...

Devcon is not as high rated for temp and is about the same as permatex.
 
masculator said:
You make less sense with each post!!!

you should be getting a minimum of 145 psi on a worn out 088/ms 880. a stock ms 361 that gives 85 psi will not run and would be minimum 160 psi of compression!

Think you need to make more sense! how the fark do you get a gouge in the Crankcase chamber of a cylinder???? It makes no logical sense the cylinder does not have a crankcase chamber!
Click to expand...

I use my 361 every day, come show me how it dosn't run.
Cylinder in question with gouge I got for free, had broken piston between rings, peice obviously got below piston.
Two strokes compress air/fuel in crankcase to push it up. Therefore it is a chamber of sorts and is below combustion area of cylinder. Dont like my posts stay off the thread
 
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If you've done what I think you've done (cut a feed from the roof of the inlet port to create a boost port above it) it won't work.

To make a port above the inlet port work on a piston port engine it's feed has to be taken from the crankcase and fed around the inlet port without actually cutting into it.

If you need a new cylinder Matt/MCW can supply aftermarket ones or you can source one from the US.
 
Rusty-880 said:
I use my 361 every day, come show me how it dosn't run.
Cylinder in question with gouge I got for free, had broken piston, peice obviously got below piston.
Two strokes compress air/fuel in crankcase to push it up. Therefore it is a chamber of sorts and is below combustion area of cylinder. Dont like my posts stay off the thread
Click to expand...

Not saying I don't like your threads just saying that what you are saying makes no sense!

Trying to make sense of what you are dribbling so I can help you! wanna be a tool thats fine! but no ms 361 will run with 85 psi compression and stock they come out with well over 160 psi compression not 85!

so is it a cylinder (top end, that the PISTON goes up and down in) or a cranckcase (bit the crankshaft spins in) that you are referring to?
 

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