Stihl MS250 Won't Run

[Stillrunner]

Just signed up today to hopefully get help solving a problem with my Stihl MS250 chainsaw. Last fall I scored the piston by pushing the saw hard with a dull chain. I cleaned the cylinder and put in a new piston. I replaced my crank seals and pressure checked for air leaks. The engine had no air leaks. I also replaced my intake boot. Once I got it all back together the saw would pop on full choke and then run strong for about 3 seconds on half choke and then die out. Thinking it might be my carb I bought a replacement carb and installed it, along with a new carb to boot, gasket. Still have the same problem. I'm going to replace my impulse tube now but running out of time to get this saw working and asking that anybody, make any suggestions as to how to solve this issue.

Thanks in advance.

 

[GPX433Todd]

New fuel line from tank to carb?

 

[a. palmer jr.]

That would just about cover everything on the intake part unless you bought a new carb or line that was a factory reject. Other than that possibly an ignition problem but I'd still think it's in the fuel system. I doubt it ran long enough to think it might be a tank vent problem.

 

[Wood Doctor]

You are going to hate me for saying this, but it could be the cylinder that you cleaned but did not replace. This sounds like a compression problem that was not solved by the new piston and rings, especially if the engine refuses to idle correctly. If the cylinder is out of round, the new piston and rings will not save it.

Test for compression to verify this. Chances are you are less than 110 psi. If so, the saw may start and run for awhile and may be OK at the top end, but it won't idle worth a hoot.

 

[Jed1124]

99% sure there is no impulse line on that saw

 

[Wood Doctor]

99% sure there is no impulse line on that saw

There is an impulse hose on the 025 engine. 1123 141 8600

 

[chainsawman2011]

pull flywheel off and make sure the keyway is not sheared. also check to make sure you have correct coil spacing. if that's not it I would say you need a new cylinder

 

[Jed1124]

There is an impulse hose on the 025 engine. 1123 141 8600

Huh. I could have sworn a 025 I worked on didn't have one. Bad memory. Thank you for the correction sir!

 

[Stillrunner]

Thanks for everyone's responses. I can assure you, this saw has an impulse line. It's original and although I checked it for cracks and leaks, it's time to replace. it. I also ordered a new fuel line and filter. As far as compression goes, I will check that with a gauge. However, once I got the saw back together I figured compression was not an issue due to the (new) extreme resistance felt when pulling the starter rope. While I have the saw apart I will also check that the key is not sheared and the coil has the correct gap.

One thing I forgot to mention is that this starting/running procedure can be repeated several times, consecutively. Full choke the engine pops right away. Move choke to half and engine runs strong for a few seconds and dies. Move choke to full, engine pops. Move choke to half and engine runs strong for a few seconds and dies.

 

[a. palmer jr.]

It might be a carburetor issue. I had an 025 that wouldn't run very well despite several cleanings so I bought one of the cheap Chinese ones on ebay and that cured the problem. I think the carb cost about $10 and it included free shipping.

 

[Chev727]

Have you played with your carb settings much?

 

[a. palmer jr.]

Have you played with your carb settings much?

I think the one I had just had one screw, when I saw what it was I started looking for a conventional design and I'm glad I did. I cleaned the other one but didn't help. I've had a few little Homelite saws that just had one screw and I usually look around for the better carb for them too.
As for playing with the settings, I usually find out what the factory settings are supposed to be and work from there. For some saws the factory setting is perfect and for others you have to play around with them but if the carb is right you shouldn't have to go too far from initial setting..

 

[Cope1024]

It might be a carburetor issue. I had an 025 that wouldn't run very well despite several cleanings so I bought one of the cheap Chinese ones on ebay and that cured the problem. I think the carb cost about $10 and it included free shipping.

I did the same thing, and got a carb with the high speed adjustment.

 

[Stillrunner]

I bought and installed a new, inexpensive Ebay carb. Saw acts the same with either the original or new carb installed.

 

[drf255]

What are your needles set at on the carb?

 

[Festus]

As already said, check the fuel line from tank to carb. If I remember correctly, it's a pain to get at and a pain to replace, but it is very likely your problem. Bend it and the cracks will show up.

 

[a. palmer jr.]

What are your needles set at on the carb?

Most of them are set at one turn out from lightly seated. You can play with it a little from there but not too lean or it'll fry a piston..

 

[Stillrunner]

My carb needles are set as per the instructions on the side of the chainsaw, plastic cover. I have adjusted them, 1/4 turn at a time but never found a setting that solves my problem.

I have a new fuel line and filter, impulse tube and carb to cylinder boot coming. I will install all those parts this weekend and then report the results.

Thanks for all your help.

 

[huskihl]

Make sure your impulse and fuel lines go to their respective ports on the carburetor

 

[drf255]

Make sure your impulse and fuel lines go to their respective ports on the carburetor

Impossible on this model.

The impulse line connects to the saw body and seals to the carb at the carb gasket. You can't see it I the carb area.