Old Stihl 025. Cranks but won't run.

[N80]

I have an old home-owner grade Stihl 025 that I inherited from my Dad. It has worked well for years. Last year when I tried to use it it would crank, run for a second and then stop. After that it would not crank unless it sat for day. Repeated same thing many times. Drained all old gas/oil out. New gas/oil in. Same behavior.

It has now been on the shelf for over a year since I have a larger newer Stihl that gets most of the work.

However, this is a decent small saw and I would like to have it running for small chores.

Any ideas on a simple fix? I am fairly mechanically inclined but have never worked on a chainsaw motor and don't have a lot of time to do so. Don't want to spend several hundred at a repair shop since the saw probably isn't worth much of anything. (Also, for some reason the main local repair shop will not work on Stihls. Not sure what they do work on.)

 

[Egon]

Clean the air filter and exhaust ports. Open the low & high speed a little, spray WD40 in the carb and see what happens. You can keep adjusting the jets but do remember where they were originally.

As it’s an older saw it may have reduced compression. If it pulls easy this may be the case.

 

[Richard]

You drained the oil gas out before or after it acted up? (I'm wondering if your carb might be gummed up inside)

I always try (and sometimes forget) to run mine dry before putting it up.

 

[ericm979]

I would not recommend messing with the carb adjustments or spraying WD-40 in the carb. Starter fluid or few drops of premix would be ok if you think gas is not getting to the engine. Usually the problem is flooding though, unless there's a problem with the carb or impulse line. (part of the carb is a fuel pump that runs off changes in engine vacuum via the impulse line).

Starting but not running means that the ignition is probably ok.

I'd pull the muffler off and inspect the exhaust side of the piston. Post pics. Poor starting/running can be from partial seizure or piston damage.

 

[lman]

Replace the fuel line. Old fuel lines don't like new gas.

 

[N80]

Thanks guys. A couple of things for clarification:

1) The problem first happened with old gas.
2) Ports and piston inspected. All look okay.
3) Air filter cleaned.
4) Compression seems okay.
5) I've flooded Stihls plenty and this does not seem to be a flooding issue. At least not the typical kind.

I agree that it does not seem like an ignition problem since it will crank and run for about 10 seconds. Hoping it is a gummed up carb or fuel line. Fuel lines are probably original or they may have been changed once. Saw is at least 20 years old. Heavy and sometimes abusive use when used but not used all that often. I replaced the fuel filter that is in the tank once fairly recently. It looks clean.

 

[N80]

Just tried it again for the first time in probably six months. Based on cord pull the compression is fine. It was cold. Cranked like normal after a few pulls. Idled for a few seconds. Bogged a little at first bt then rev'ed like normal with the trigger. Sounds good as new. Then just stops dead. This time I was able to crank it again with the choke setting at halfway. Ran for a second then stopped. After that, nothing.

 

[monkeyduster]

Small crack or pinhole in the fuel line can cause this kind of problem.

 

[Egon]

It would sound like fuel is not getting to the carb or through the carb. Try adding some fuel conditioner to the fuel. .???

Don’t worry about adjusting the jets but do make sure you remember where they were. The low speed is adjusted so the saw will idle without the chain turning. The high speed is more critical as too much can result in over speed. Setting on this one means you want power when cutting but no over speed. Most shops probably set this by ear. WD40 will also act to dissolve some fuel varnish build up.

On the funny side: recently my husky 55 would not start. Took it to the shop and they had joy on the second pull. Turns out I wasn’t pulling fast enough on the cord. Rather embarrassing.

 

[dodge man]

You tried a new spark plug? I actually had one go bad in a Stihl MS250, which I think is a newer version of your saw. It was acting very similar to what you describe.