I have a 039 that once would run great for about a hour then slowly lose power then die. Would not start till cool then would run again for a hour. Coil was the problem.

I'm your Stihl tech


That is an old saw, not that it is a bad thing. Stihl has a check list that will find any problem in minutes. That problem I would check for spark immediately after it died. If it has spark you can check compression when it's cool, and again after it dies. 100psi or less it has issues. There are several possible problems. It could be a lack of crankcase pressure and once it warms up it can pump fuel because of an air leak.

Vent is probably most likely, if that isn't it, rings is probably next. I've had a couple of small Stihls that were sucking air, they would run when started, but ran too lean and would get hot and sieze after a couple minutes. Let them cool down and they would start again. These were the newer, throw away, small Stihls that cost more to rebuild than to buy another. I just ran them on the fourwheeler or snowmachine to cut blowdowns out of the trail until they got real bad. Could usually cut a couple logs out of the trail before they got too hot to run. Got another year or two out of them that way and when they got where they would seize before I had a log finished cut out of the way I tossed them. Had a 660 and an old 41 that did the same, rebuilt the 660 but couldn't get parts for the 41 so it became a parts saw for a friends 41.

Head gasket

I’m curious to find out what the problem is. Majority vote is vent issue, but the forum Stihl tech doesn’t even mention the vent on the list of probable problems. Very interesting!

It starts right up again

I suspect you mean it CAN'T pump fuel because of an air leak.

That sure could be the problem.
Yesterday I got a fuel tank cap from an 031. It did not solve the problem. So I ran it with the cap slightly cracked open. No JOY !!

I finally got a flashlight and small brush in the tight space where the impulse line runs and.........it appears to be fine........but might have a crack I can't see.

I pulled the filter/pickup out of the tank again and disassembled the filter. There USED to be a foam insert in there but at this point there is only about 10% of it remaining. I am going to pull the carb apart again and see if some of that material is blocking the hole under the needle valve.

I also followed Dirt's suggestion and pulled the plug right after it quit. The plug was bone dry but a very nice color. About like the background color on this forum.

I'll try the compression check today Patfundine.

Thanks to all with ideas

Do you have to choke it?

No. It fires on its own. It won't stay running at that point though so It may just be residual fumes

Sounds electrical to me. Doesn't mean it is. When it dies, does it sputter and die or die like you hit the kill switch? When chainsaws start doing some of these odd things, it can try ones faith in oneself.

It doesn't "act" electrical. It clearly starts losing power even though it continues to fire smoothly. When it finally quits it just quits ..sort of "peacefully" ))

Not a sudden stop like an electrical failure. More like slowly choking it to death.


I hear ya on faith in oneself !!

Be nice if you had a known good coil to try.
Check spark with a real spark checker, hot and cold.

Compression got low on mine. Ring end gap was huge.
New rings and the rest of the consumable parts and back to work.

Take muffler off and looky in there.
If yucky its time to tear down or move on.

Will do !!

Just buy the wife a crosscut saw.

Google the model and symptoms of what’s happening. My bet is it vapor locking from a plugged vent. Bet it runs longer with a half tank of gas than it does with a full tank? Sucks tank dry of air then stalling out. It’s something simple, I’m sure

Great saw. I put 24" bar on mine and it didn't miss a beat. Coupled with my 230 they make a great pair.

Too noisy !

But I tried with a different, vented cap and it did the same thing. I am hoping for something simple but it seems pretty complicated figuring out what that simple thing is !

My 038 would start and run but when it came time to use it, it would quit. A new fuel line and filter and so far so good.