cant get chainsaw to idle!

[tobaccogrower]

i have a sthil chainsaw. i think it's a 021 with a 16 inch bar. it has very few hours on it. i cant get it to idle! the manual says close the top carb screw all the way in then open 1 turn. did that and it dies soon as i let off the throttle. it seems better when i close the top jet to like half open. the plug looks good, gas is ok and muffler isnt cloged. i guess i'll get a new plug and go from there. any other ideas? thanks..... james

 

[Cummins Pilot]

I'm not familiar with that particular chainsaw but a carb is a carb for the most part. That top carb screw as they call it should be the air screw adjustment. The air screw only adjusts the mixture in the idle circuit. Some carbs are different but most of the time turning the screw to the left allows more fuel to flow. This is helpful at cold start up but once the engine is at operating temp it will die after you come out of the main jet range and into the ilde range. It floods itself.



Was the engine at operating temp? To correctly adjust the air screw the engine must be at operating temp. Most carbs seem to like the airscrew 1. 1-1. 5 turns out (left) from the bottom. If it runs better at . 5 turns go from there.

 

[TORQUE THIS]

Take it somewhere and get it adjusted. I'd be happy to do it if you were near by. You can get it close, but if you are off a little bit, you can burn it up. Have seen it many times.

Adjustments are 1. 5 turns out. Turn in the idle screw a little also to keep the saw running while you check the high and low speed adjustments.

The high speed adjustment is closer to the motor, they should be labeled on the carb with a simple "L" and "H".

To make a basic adjustment, you need to get the high speed set first. Start the saw and run at WOT. Turn the high speed screw in till it sounds like it is really screaming. Remember that spot and slowly back it out till it sounds like it is loading up or going to stall. From there turn it in about 1/4 turn and you should be good.

The slow speed is just the same as the high speed. At idle follow the same steps.

Once the slow spped is set, back out the idle screw till the chain just comes to a stop. You might have to hit the throttle a few times after backing out the idle screw.


This should get you close, but I would really let a shop adjust it correctly.

 

[Cummins Pilot]

Torque, those chainsaw carbs have adjustable main jets via a screw, or is it changing the height of the needle? I've never worked on a chainsaw carb. I sure wish all the dirtbikes & snowmachines I work on could adjust the main circuit that way. Sure make my life easier. Nothing like taking half the intake out of a snowmachine just to change two or three jets.

 

[TORQUE THIS]

Yup, 3 screws, high, low and idle. Very easy once you get used to it. Helps to have a tach also to check WOT.

 

[phloop]

Yup, 3 screws, high, low and idle. Very easy once you get used to it. Helps to have a tach also to check WOT.

:{ The new saws no longer have a three screw idle adj. set up thanks to the Kali/Fed nazis due to their clean air act. The new saws only have high and low, no idle.



My father and I own the same model Stihl saw, only the name has changed, we bought them a year or so apart. I have a MS 250 while I think his is an O-25 or some such thing. The only thing different between his and mine other than the number/name change is the fact he put an older carb on his that has the three adjustments on it. His saw screams compared too mine and he can out cut me no problem.

 

[tobaccogrower]

my saw only has 1 adjustment screw! the otherscrew moves the throttle linkage open to adjust the idle! i looked for a high screw but theres not. i think i'll take it to a dealer! thanks... james

 

[Alphacowboy]

stupid question, but did you check the air filter?

 

[tobaccogrower]

air filter is ok.