Stihl 041 AV lost power, backfires through carb.

[NWTimber]

Hi all,

My first post here! Great forum!
A friend gave me this saw not running, but compression felt great and I had it running after disabling the kill switch and installing a new plug. It was a bit slow to rev and lacked power it seemed, and while making my first cut, the clutch shoes broke free and bound up the clutch. I removed the pieces and decided to try just running a metal-to-metal clutch and that worked. I make a few more cuts with the saw.

Then, I decided to try to make it run better by removing the partly clogged spark screen and sprayed in 'Blaster LMT (lawn mower tune-up) through the spark plug hole to clean the carbon off of the piston face. I also removed the carb and checked all the intake components around the intake manifold, then reassembled, finding no leaks or warping. New impulse and fuel line/filter. Original lines looked fine, and tank was clean BTW.
Well I think I put too much of the LMT in, which got around the piston and flooded the saw when trying to restart. Pulled plug and blew out all that I could, then got her started again.

I had also reset the carb H and L to 1-turn out, and now it starts and sounds the same, BUT IT WONT REV UP AND SPIN THE CHAIN, AND BACKFIRES THROUGH THE CARB WHEN GIVEN THROTTLE. Feels like a chain brake is on, and I've tried various carb settings with no success.

Not real familiar with chainsaw electronics yet, but I read here to check the flywheel key. So I pulled the finned flywheel and see that there is a Bosch drum-type assembly beneath it. There is one small key that I can see, which looks fine, and the whole assembly feels very locked to the crankshaft (no play detected.)

To go further, I'll have to find out how to pull this drum assembly off somehow. And I believe that my buddy had already cleaned &/or replaced the carb, but not 100% sure. I don't understand what I could have done to cause this new condition, which seems to be a timing issue.

Any ideas?
:confused2:

 

[darren_palms]

Could be a timing issue...did you check the gap between you coil and flywheel?

 

[pioneerguy600]

Your flywheel may have sheared its key.

 

[NWTimber]

I've got to find a way to remove the drum / flywheel to check the gap.. still not sure how to pull it without a special tool that engages the three holes that are used to hold the finned aluminum flywheel to the drum. Does that make sense?

 

[darren_palms]

Your flywheel may have sheared its key.

I agree also...I sheared the key on my 2100 and it wouldnt start and it would backfire .

 

[pioneerguy600]

I agree also...I sheared the key on my 2100 and it wouldnt start and it would backfire .

Usually it is a sheared key that causes backfire, I have never been able to adjust the air gap in or outward to cause backfire. The module could be going out if it is electronic ign, if it is points then again I have not seen them off so much they would cause backfire but it would be worth checking the condition of the contacts and then resetting the points gap.

 

[R/C Pilot]

Try a new spark plug.

 

[NWTimber]

View attachment 280773

Here's a couple pics of the flywheel / drum.

 

[pioneerguy600]

I've got to find a way to remove the drum / flywheel to check the gap.. still not sure how to pull it without a special tool that engages the three holes that are used to hold the finned aluminum flywheel to the drum. Does that make sense?

To pull it properly you do need a puller that connects to the flywheel by those three holes and a center bolt to push on the crank end. The flywheel can be removed by holding the saw up by the flywheel and then hitting the crank end a sharp blow with a brass hammer or brass drift and a hammer. If you can find a helper to hold the flywheel it makes the job a lot easier. The crank can be damaged easily if this route is used and not done properly.

 

[2rod511]

Sounds like it is out of time. I would pull the flywheel off even if it has sheared the keyway you can line it back up by marking the flywheel and the crank shaft and tightening the hell out of it. The crank shaft is probably tapered and will hold the flywheel still without the keyway, if you feel frisky then advance the timing slightly when you reinstall the flywheel. I pull flywheels by backing the nut off until it covers the last few threads on the crank then placing a prybar under the flywheel and pry on it while I slap the flywheel nut with a hammer.

 

[NWTimber]

View attachment 280775View attachment 280776View attachment 280777View attachment 280778

More pics, and thanks for the advice. I'll attempt to get that flywheel off and check things out. How do I tell if this is points or electronic? Never messed with points before.

 

[2rod511]

The flywheel has a magneto that fires the coil when it passes by it, but from the pictures it appears you are working on the clutch not the flywheel you need to flip that biatch over.

 

[Kenskip1]

Does it have spark?Even if it is a bad key you should still have spark.Pull the plug and lay it on the metal housing and give it a pull.I would replace the plug as mentioned, Ken

 

[R/C Pilot]

The flywheel puller for an 041 threads into the hole around the shaft and nut. It's around 20 mm with a bolt in the center of it. I recently had a Jonsreds 49 SP that idled good but would not rev up. A new plug and its cutting fine.

 

[pioneerguy600]

View attachment 280775View attachment 280776View attachment 280777View attachment 280778

More pics, and thanks for the advice. I'll attempt to get that flywheel off and check things out. How do I tell if this is points or electronic? Never messed with points before.

I do believe all the 041AV`s are electronic ign. The 041 Wood Boss had points ign.
Your saw is an 041 AV so it most likely has an electronic ignition.

 

[R/C Pilot]

041AV came in both points and Electronic. My 041 AV Farm Boss has points. Electronic models said so on the air cleaner cover.

 

[2rod511]

Am I crazy or is the OP trying to remove the clutch instead of the flywheel. From the pictures and some of his earlier posts it sounds and definitely looks as if he is attempting to remove the clutch.

 

[R/C Pilot]

I just looked at your pictures. A very nice looking 041 AV . ( Pionts model ) But the points are under the starter cover.

 

[NWTimber]

My first two pics in the early posts show the flywheel that I'm working on.

The later four pics are just general pics that also show the clutch after the shoes grenaded.

I will try a new plug, even though this one is new. I'll get this flywheel pulled Sunday night I hope! Probably points, because it doesn't say electronic on the top cover.

 

[R/C Pilot]

Reading your first post in this thread you said you reset the H and L screws at 1 turn each. My 041 AV manual says the factory settings are H = 3/4 and L = 1 1/4 . If you are going into the mag keep in mind that any adjustment of point gap changes the ignition timming and that prosses is done through the windows in the flywheel without pulling it. Your 041 AV looks to be in very good condition and you say it starts and idles makes me think the mag is ok. There are timming marks on the flywheel and case to verify timming by hooking up a meter to the kill lead. Good luck with your project.