Stihl FS 250 engine troubleshooting

[austin11235]

Hey all,

My first time posting on here, but I have browsed the forums many times looking for answers to other questions. Thanks in advance.

I have a FS 250 brushsaw that starts fine, idles fine, but won't get up to speed. When I depress the throttle, it just kind of makes a low growl and the blade won't start spinning (the blade spins freely by hand).

I noticed the exhaust was oily, so I took the cylinder head off to see if it was all gunked up inside. It was not, but I did notice some buildup on the top edge of the piston, while the piston crown was covered in a dried, oily scale. I also cleaned the carburetor thoroughly, as well as the air filter. It's all back together, and is still behaving the same way.

Could this be a compression issue?

 

[backhoelover]

the coils could be the problem. the coils have three stages in them. get a coil off ebay and try that. could still be carb. have you tried adjusting. also check the screen inside the carb. hold the screen to the light and make sure you can see through it

 

[backhoelover]

here is the service manual

 

[GrassGuerilla]

Dumb question maybe, but did you pull the muffler and check the exhaust port? Carboned up exhaust will cause that. Classic really.

 

[sliderulacuracy]

Hi

mine had similar symptoms, after, lots of trial and error, i finally put on a new muffler, difference was night and day.
apparently the 'condensate' gunks up the holes in the exhaust baffles and you then can't get it hot enough to clear them.

the new muffler weighed much less that the old one as it was full of 'tar' .

you might give that a try.

 

[GrassGuerilla]

Hi

mine had similar symptoms, after, lots of trial and error, i finally put on a new muffler, difference was night and day.
apparently the 'condensate' gunks up the holes in the exhaust baffles and you then can't get it hot enough to clear them.

the new muffler weighed much less that the old one as it was full of 'tar' .

you might give that a try.

This can be tested by simply removing the muffler and briefly starting it. Don't run it long, just long enough to see if it piss revs now.