Stihl 025 won't idle, low power, tried almost everything???

Treedawg

New Member
My super loyal 20y/o 025 chainsaw has had a hard time idling for about a year but ran fine otherwise Suddenly it's bogging and won't run with anything more than about 50% of its normal strength and seems to be smoking just a bit more than usual.

Always run non-ethanol fuel, the compression seems strong and the motor's not making any odd mechanical sounds when it does run so I checked the plug and found it totally fouled.

Figured the carb probably deserved some attn after all this time so I just installed a brand new carb, spark plug, and replaced all the fuel lines and filters including the air filter thinking that'd definitely do it. No change and the fresh plug looks wet after struggling with a 60sec run.

Read somewhere that bogging might be a blocked exhaust spark arrestor screen so I pulled the exhaust and it was oily and a bit wet but otherwise completely unrestricted. Suspecting a bad batch of fuel mix I very carefully mixed a new batch...... no change. Saw still barely starts and only runs at about 50% power.

I didn't replace the coil yet because the spark looked pretty strong but I have a new one coming anyway.

If it was a bad crank seal I'd think it'd be sucking air and running lean rather than rich but maybe it's something else.

I'm good with a wrench and usually good at trouble shooting but I'm totally stumped and hope I'm missing something obvious that other 025 owners/techs can aim me at. Thanks for ANY sound leads. Mike
 

evo

Well-Known Member
Wet oily exhaust and wet plug might point to the coil going out. Basically lack of spark.
 

Treedawg

New Member
Appreciate your post. The new coil should arrive today and I'll be sure to post here until the issue's revealed so the next guy will know what we found. Thanks for any other input by 025 owners or gurus of mystery Chainsaw issues.
Mike
 

Treedawg

New Member
Well, I changed the coil (along with all the other items listed) and it still behaves the same. Runs fine for 2-3 seconds then the power goes down significantly and it becomes nearly impossible to keep running. Tried adding a bit of choke while it's running but that just stalls it instantly. Also tried loosening the gas cap with the thought it's not venting (even though it has a new vent) but that made no diff.

That's about the end of my bag of tricks. All I can hope is somebody here might have an answer to my mystery.
 

Treedawg

New Member
Don't think it was but I'll check it. Can't really say I'm familiar with the impulse line but I was pretty careful to replace each line as it was on the original.
Thanks for the lead
 

Treedawg

New Member
The intake boot and impulse lines checked out ok, so I tore it down to the motor core and handed it to my Sthil guy for a new set of crank seals. I'll know by the weekend and will post my results.
 

Treedawg

New Member
Feeling sure of what the real issue had been narrowed down to, I got new crank seals installed, blew out any possible crud in the brand new carb, put it all back together and that's NOT it either.
smiley_furious
It'll start and struggle to run, just as it had from the beginning, but it's still running way too rich. I even took off the muffler and ran it with no change in the symptoms.

Pulled the air cleaner and started it and raw fuel droplets are visibly being blown back out the intake.

Maybe it's a bad set of rings causing blowback?? On the other hand the compression is good.

I talked at length with the Saw mech who asked me to bring it back fully assembled, rather than just the powerhead, so I gave up and just dropped it off this morning, fully assembled with all the new parts installed from all the former theories.

Posting this saga in the hopes of saving someone else my grief. I'm sure it'll all seem obvious when the mystery is solved.
 

Treedawg

New Member
whiteflag_smiley
whiteflag_smiley
Well, I surrendered and took it to the shop. Hind sight is always 20/20. My 1st inclination was right. My Sthil shop said it was a bad carb from the very beginning, but (as my luck goes) I had gotten a brand new one that was defective and the gremlin chase was on.
smiley_devil
smiley_devil
Don't ask what was wrong with it, I absolutely threw that defective turd as far as I could.

The up side is that my tough old friend the 025 is in nearly new condition with seals/lines/coil/plug/carb/filters/etc.... and it got a through cleaning and some much deserved TLC.

Hope my post details help somebody else chasing an elusive gremlin...... Sometimes a brand new part is just bad too. Rarely, but sometimes.
 
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