I have a O21 stihl chainsaw and it stops running after 15 to 25 seconds. I have looked at the spark plug and it seems fine. I cleaned out the air filter and still have the same results. Does anyone have another idea where the problem is-thanks

Alex Koplin, July 2005

its possible that you have an air leak. the unit needs to be pressure tested to make sure there is none.

Robert, January 2013

ive got the same fault has anyone come up with the actual solution yet. Ive stripped down the carb, fuel filter , air filter, plug, ....leaning towards the starting coil...

joolz, March 2011

There could be several reasons for this. I had a similar problem with a chain saw I had and it turned out to be a clogged muffler. It could also be a problem with the fuel line or the fuel itself. Most chainsaws have a weighted filter on the end of the hose in the gas tank. If there is a break anywhere in the line to the carburetor you could be pulling in air instead of gas once it starts. I think, since it starts and runs for a short time I would check the muffler first as it sounds like it is getting gas. Another problem to check for is the primer bulb - make sure it isn't cracked as this would change the gas/air mixture.

Len, July 2008

Sometime you gotta wonder why some of these guys keep advising to go to a shop...is this not a how to mend it site....?????

thanks for the advice, September 2007

how old is your saw.. I have had stihl for about 8 years..they are simple tools if you understand the 2 stroke concept. Check the fuel filter..they are recommended to be changed every year. If you get to whits end. Throw it in your truck ( or car) and take a drive..find a stihl dealer in the country..the will take a look at it for nothing. I have never had any trouble with chainsaws but my blower is surging.. haven't got into it yet..probably stuck valve..but check fuel filter..and make sure you dump the old gas..might have water in it

KodiakKen, June 2007

Although the other answer could be it, you may want to check the fuel filter first, they often clog in 2 stoke motors (when the oil dries on them). It is most likely in the fuel tank. They can be replaced (and I have even cleaned them).

Harry, September 2005

the high and low running jets need to be set up properly. If you haven't done this before it is best done by a Stihl service engineer as there is a danger of over reving the engine and blowing it completly. the screws used o adjust the running jets are normally found to the left of the air filter and are located in deep holes, you will need a small flat head screwdriver with a long shaft to get at them. L is the low rev running jet and H is obviously the high one. If you mia adjust these the saw will not run smoothly and is therefor more prone to kickback or running chain etc Remember it will only take a fraction of a second to lose a finger and not much longer to lose a leg or arm.
Good luck!!

ben, July 2005