Stihl Chainsaw - chain keeps moving even at idle

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I'm not an expert on chainsaw mechanics, so thought I'd ask for some suggestions from those of you more familiar with these machines than I am. Basically, I have a Stihl 029 Farm Boss chainsaw that I've had since '98 or '99. It has been, and still is, a great saw that has seen a lot of duty in various disaster relief operations (post Hurricane Katrina, 2011 southeast tornado relief, etc.). The only thing wrong with it is that sometimes after I cut some logs the chain keeps turning even after I release the trigger to bring it back to idle. Sometimes blipping the trigger will get it to stop, sometimes not. This is rather dangerous and I would like some pointers on fixing it myself if at all possible (I'd rather not take it to the shop as that is expensive). I find myself often holding the chain against a tree limb to get the chain to stop.

So what do you think is causing this? High idle speed? Bad clutch? Or both? Would adjusting idle fix this and how do you do that on a chainsaw? I'll also mention that I always store this saw without fuel in it; I drain the fuel out and run the carburetor dry and then put it in storage.
 
I have a 6 year old Stihl MS250 that did the same thing. I think the ethanol in the gasoline is to blame for jacking up the carburetor. My father in law was able to locate some ethanol free fuel last summer when we had 30 trees to drop at his place. The saw ran much better after the first tank of straight gas. It could be a coincidence but, I only run ethanol free fuel through it now.
 
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Assuming the engine is actually returning to a normal idle RPM and not high-idling, then its a centrifugal clutch problem. Either the clutch is gummy and sticking, or the return springs are weak from excessive clutch slipping, which is usually from cutting at too low RPM. I'd pop the chain cover, and start with a good cleaning on the clutch assembly. They're usually fairly easy to replace, a 4-leg puller can generally be set up to get them off, though I've yet to have to mess with the clutch on my own Stihl.
 
sounds like a high idle problem? if tapping the trigger makes it stop sometimes is it because its idling slightly lower?
 
Does it idle high? if not...

+1 on the clutch spring.

If it idles high you may have an air leak.

For tips on chainsaw adjustments and more reading join Arboristsite and post it in the chainsaw section. (My name is Plan-b on arboristsite)
 
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First thing to check is just that the idle is not set too high, period. If the idle is set where it should be, move on from there and check the clutch. Start simple first though and check the idle.
 
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So what do you think is causing this? High idle speed?
It could very be an idle speed issue. So start with the basics here.... idle speed

Best way....With the saw warmed up fully, hook up a proper tachometer and adjust (LA) screw found on the filter cover to 2800 RPM.

Back yard or out in the woods way....With the saw fully warmed up turn (LA) screw counterclockwise until chain stops running. Than turn the screw another 1/4 turn in the direction.

Warning I would not touch the two H or L mixture screws at all! If you are asking this question. Because you can burn or seize a chainsaw up fast if you don't fully understand these two screws.
 
Thanks for the advice, guys! Interesting about the ethanol gas, InhalingBullets, as that is what I've been using in the saw from day one. I do have some ethanol free "pure" gas now for my OPE, so will try that approach first. This is not the only piece of Stihl equipment I have that behaves this way; this also happens with my Stihl FS45 grass trimmer, whose head will still spin even when at idle. It's not so much of an issue with the trimmer but it behaves similarly to the saw (and probably has a similar engine design). I use the exact same gas mix for it as for the saw, so the ethanol gas might be it. I'll try that first the next time I use the saw and see if that helps; if that doesn't work then I'll try adjusting the idle speed as Hirev suggested. If that doesn't do it it might be time to look at the clutch. I try to keep the saw running at high speed when cutting but sometimes it gets slowed as it goes through a tough section of the log, but I usually then try to lift up on it to get it to speed up again. But this saw has probably got 100 hours on it or more over the years, so maybe the clutch is about due for some maintenance or replacement.
 
My 041 Farm Boss is old. It doesn't have a chain brake. Does yours? I lost the idle setting screw 25 yrs ago. It dies if I'm not on the gas. The saw starts easily, so it is no big deal.
 
raffy,

I doubt your clutch is worn at 100 hrs unless it has had some serious abuse. My Dad has a small "fleet" of Stihls. One of them in particular has cut 3000+ cord and I used it working full time one summer clearing stone walls on and old farm and cutting up firewood-and I believe the clutch is still original. None of his other high hour Stihls have had the clutches replaced either.
 
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I do have a chain brake on this saw, and it does work when it's running. It is hard to start with the brake on though, so I always start it with it off; I don't like stressing the clutch with it on when starting. I do have to be careful when starting it with the brake off as sometimes it revs quite high before settling down to idle, allowing the chain to turn. My problem usually occurs after I've been running the saw a while under load. I appreciate Reddog's comment on Stihl clutches being generally very durable, as I wasn't sure what to expect in that regard. So in my case the clutch probably isn't the problem as I've definitely not abused it and I try to minimize the wear and tear on it as much as I possibly can. I'll try using pure gas from now on with this saw and see if that corrects this problem. Stihls sure are great saws; mine has never let me down in the years I've owned it.
 
Do you have the chain tensioned correctly? A properly tensioned chain will provide a very small amount of resistance that might be the difference between a chain moving at idle or not.

If you have a sprocket nose bar, the chain should have NO slack between the chain and bar bottom. I teach people to adjust the chain tension to the point where the chain touches the bar bottom, but you can still grab the chain and rotate it by hand. Its really a "feel" type of thing and if you are not sure, go to a dealer and have them teach you.

A non sprocket bar should have just a tiny bit of slack between bar and chain. Non sprocket bars are very rare these days.

Also, the chain brake engaged should not affect starting. Be very careful with your procedure. Don't rev or run your saw too long with the chain brake on....it can kill your automatic oiler.

If everything thing else is right with your saw, then the idle speed adjustment is what keeps your bar from rotating (as already mentioned).
 
If you haven't already done so, remove the spring clip and sprocket to clean out the clutch & drum. (clean and lube the idle bearing here also) This area can get sawdust in it and perhaps that is what is causing the clutch to grab at idle. This is a quick 10 minute job to clean it out. I do it whenever I am cleaning up the bar, sprocket area, or changing chains.
 
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Yes, I did have the chain tensioned such that there is no slack in the chain, but after a couple of hours of cutting logs there was a slight bit of slack. That might also be a contributor as well. I'll definitely remove the sprocket and try to clean out any junk that might be in there, haven't done that yet. I've never done that before so maybe that could also be a contributor as well.

So for anyone else that might experience this problem, here's a summary of what to look for based on peole's comments here:

1.) Try to use ethanol free gasoline, if you can find it, for your chainsaw, and other OPE for that matter.

2.) Make sure idle speed is correct when using the proper fuel mix for your saw.

3.) Make sure chain is tensioned and snug against the bar (but not too tight) such that the chain has a small resistance to being moved.

4.) Remove drive sprocket and clean out clutch and drum to remove any sawdust or other matter that might cause the clutch to grab prematurely.

Any additions?
 
Bad clutch spring or high idle due to lean condition. If you have to ask you should take it to the dealer.

Try turning the L screw out a 1/4 turn to richen the idle mix. You could have a leaking intake boot or crank seal, so it really should get checked out by a pro.
 
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