stihl 025 3 screw carburetor

[rreup]

I just installed an aftermarket carb on my stihl 025. The new carb has 3 adustment screws. I assume the 3rd screw is the high speed adjustment. Does any one have info regarding how to adjust the 3 screw carb? It started right up, and seems to run fine, but I don't want to over rev.

Thanks   

[grweldon]

I would think one would be the High RPM mixture, one for the Idle mixture/air bleed, and the third would be a throttle stop to adjust the opening of the butterfly at idle...I've worked on a lot of small engine carbs but this is a common arrangement...

[dougand3]

Welcome. There are good videos on you tube - "how to tune a chainsaw". The L and H screws will normally be labeled L H. The L is always (maybe there's a rare one where it's not) closest to the intake.

[rreup]

I did find youtube videos. It seems to be running great now. Thanks for your replies.

[CTYank]

There are some relatively standard principles/procedures for adjusting diaphragm carbs as found on chainsaws. Especially for the high-speed adjustment, you mess that up at peril of permanent engine damage. That happens if it's adjusted too lean. Too rich does bad things also.

If the (H) adjustment is right, the engine will "2-stroke" @WOT in the cut, and "4-stroke" when you physically lift it slightly from the wood. You'll find lots of vids on this. "2-stroke" means to run cleanly and sound "happy". "4-stroke" means to sound asthmatic/wheezing. Gotta have both. Adjusted properly, an engine will give peak power and live its longest. Once you "get it" it's simple, and trivial to check.

[rreup]

Thanks CTYank...I did find a video that had sound and a demonstration of the "4 stroking" sound. I knew that over reving and running too lean could wreak havoc with the saw, and wanted to avoid that.

Very helpful site...thanks again to all that posted