Stihl 031AV will not rev up, idle is fine

[Furu]

I know you set the high speed screw by the manual but have you played with it with the engine running and at different throttle positions?

 

[955Lincoln]

Man, with all of the work you have done in other areas and the fact that the problem showed up so quickly I'm gonna stick with my ignition theory. Does the saw say "electronic" on it or have you ever had the flywheel off? A good looking spark while pull starting doesn't mean it stays that way while running. I'm not familiar with electronic ignitions on saws but I would suppose they can develop intermittent problems as well, such as a coil breaking down or internal component failure.

 

[JimLev]

I know you set the high speed screw by the manual but have you played with it with the engine running and at different throttle positions?

I have tried adjusting the high speed screw and it really doesn't seem to do much at all unless it is screwed in too far and then the engine stalls.
Adjusting the low speed screw seems to do what it's suppose to.

 

[JimLev]

Man, with all of the work you have done in other areas and the fact that the problem showed up so quickly I'm gonna stick with my ignition theory. Does the saw say "electronic" on it or have you ever had the flywheel off? A good looking spark while pull starting doesn't mean it stays that way while running. I'm not familiar with electronic ignitions on saws but I would suppose they can develop intermittent problems as well, such as a coil breaking down or internal component failure.

It does say 'electronic" on the top cover. I have never had the flywheel off.
Yes, a good looking spark with the plug out can go bad under compression.
It starts up like a champ, but the engine speed won't even pick up by 500 RPM when you give it gas.
If this saw had a conventional points and condenser ignition I'd change the condenser.
Not sure if there is a condenser with this ignition, guess it's time to pull the flywheel and take a look.

 

[955Lincoln]

There is something simple you could try but if the results don't improve I still wouldn't rule out a faulty ignition, electronic or not. Pull the plug wire and try to adjust it so there is about a 1/4" to 3/8" gap between the cap conductor and sparkplug. When the spark jumps across the air gap it acts like another coil and will give you a voltage boost. You may have to play with the distance, too far and it won't start, too close and you loose the benefit of the gap. I have used this trick many times to get my 2 stroke dirt bikes running again in the middle of nowhere after fouling a plug. If you get the gap just right the engine will start and run perfectly as if you just replaced the plug. After getting the engine back up to temperature and wringing it out through the gears the plug cleans itself and you can push the cap back on without having to change the plug.

This procedure could possibly troubleshoot your coil if it's breaking down but it won't help single out other components of the ignition if in fact they are bad. Still though, it's a quick easy test to see if the engine acts differently.

 

[JimLev]

955Lincoln, I'll give it a try next week when I back home.

 

[Gobblin Tom]

My ms361 was the ignition coil / timing, it took a lot of checking that I did and it took a certified stihl tech to figure out that the timing was gone. Saw runs like new now.... JFYI....

 

[JimLev]

Guys, thanks for all of the info and help. Over the winter I just left the saw in pieces on my bench.
I did buy a new set of points and a the coil wire that goes to plug for it.
At least I found out it didn't have electronic ignition.
The old points and coil wire looked and ohmed out good, the gap was good to.
I put the new points and coil wire in, then put the saw back together.
After a dozen pulls it started right up, a few tweeks on the low and hi speed screws and I was in business.
I cut wood for an hour, the saw ran great.
I can't say for sure that it was the points or the coil wire as both tested OK.
Well she's running and that's all I care about. The old carb is probably still good.

 

[955Lincoln]

Guys, thanks for all of the info and help. Over the winter I just left the saw in pieces on my bench.
I did buy a new set of points and a the coil wire that goes to plug for it.
At least I found out it didn't have electronic ignition.
The old points and coil wire looked and ohmed out good, the gap was good to.
I put the new points and coil wire in, then put the saw back together.
After a dozen pulls it started right up, a few tweeks on the low and hi speed screws and I was in business.
I cut wood for an hour, the saw ran great.
I can't say for sure that it was the points or the coil wire as both tested OK.
Well she's running and that's all I care about. The old carb is probably still good.

I'm glad you got your saw running and THANKS for getting back to us with the outcome.

I'm curious about how your ignition is set up as I'm only familiar with the older points and condenser style. So you have points and no condenser? Maybe points and a sealed module that possibly contains the condenser and coil in one unit? If there are mechanical points there has to be a condenser somewhere to keep the points from arcing.

I'm surprised you saw says electronic but has points. I picked up an older 041 Farm Boss that does not say electronic on it so that is why I'm curious. I would assume now that my saw must have a standard points ignition.

Anyway, thanks again for letting us know. :thumbsup:

 

[JimLev]

The saw does have a separate condenser and coil. The condenser isn't available so I had no choice but to use the old one, I've found over the years that condensers hardly ever fail.
I always thought the saw had electronic ignition because that what's on the front page of the manual.....031 AV Electronic.
After I pulled the flywheel off I saw that it was just the old school points and condenser.
If I ever find some spare time I probably should put the old carb back on just to see if it's good, I bet it is.
Thanks again guys for all of your help.