MS290 won't idle

John Galt

New Member
Oct 22, 2019
30
W Montana
Hi everyone,
Stove season is over and cutting has started.
My Stihl MS290 starts fine and runs at full throttle but it won't idle anymore and dies as soon as the trigger is released. It's about seven years old, months before they switched to the 291, and hasn't had any issues or work done on it. It started idling lower a couple of years ago and would die after ten seconds but I never adjusted anything. I was bucking logs and everything was as usual. I had been working for a half hour and fired it back up after moving a few rounds and it was like the chain break was on and the chain wouldn't rotate. I shut it down, cleaned and loosened everything. The oil hole in the bar had sawdust in it and might have been clogged. Since it was stopped I figured I'd adjust the idle screw and turned the low side a bit. This is when the problems started. It wouldn't idle anymore. Below are the things I've tried or verified.

The air filter is clean.
New spark plug.
New fuel filter.
Good fuel.
No ethanol ever.
Seafoam was added for all of my "repair testing" about a half tank has gone through.
Spark arrester is clean.
LA adjuster screw has been dialed around without any benefit.
I pulled the carb. The screen was clean and the diaphragm looked ok and was flexible. I sprayed cleaner on everything and into the tubes.

After each of these steps I tested and there was no improvement at any stage.

The high and low adjustment screws just spin and don't have stops, not sure if that is an issue. I know they have protections to keep them within a safe range but everything I see says to turn until it stops and then back them off. Mine don't stop.

Any thoughts?
Thanks
 

brenndatomu

Minister of Fire
Aug 21, 2013
4,957
NE Ohio
So did you get the chain freed up then? Or at least the clutch to spin freely?
Can you get a good pic of your screws? What do the screw heads look like, brass? It almost sounds like someone has clipped the stops on the limiter caps off and now the caps are stripped as far as their connection to the screw head (often just "glued" on) If those screws really are just spinning, something is very wrong, just buy a new carb.
FYI, a new carb from Stihl is often only $20-$40...not worth screwing around with too much anyways IMO.
 

John Galt

New Member
Oct 22, 2019
30
W Montana
Yes, I pulled the chain and made sure the sprocket turned freely. Then cleaned everything up and made sure the chain turned before firing it up.
I'm the only one who has touched the saw so the screws are from the factory. The carb has red plastic screw heads that I presume are the limiter caps. They can be screwed either direction without stops.
There isn't much left to try except the carb, fuel line, and impulse line. Just didn't know if someone had an idea.
 

brenndatomu

Minister of Fire
Aug 21, 2013
4,957
NE Ohio
The carb has red plastic screw heads that I presume are the limiter caps. They can be screwed either direction without stops.
The screws are metal, so I'd bet that the screws are bottomed out and the plastic caps just broke loose before the screw came off its seat...take a small pliers and see if you can gently work those caps off the screw head...the screw head/cap are usually splined and then some loctite/glue added for good measure. They usually come off pretty easy.
 

Zack R

Feeling the Heat
Sep 27, 2017
385
Sisters, OR
flic.kr
If you turn one screw be prepared to adjust all 3 (idle, high, low). If the screws don't stop you are probably due for a new carb.
 

gzecc

Minister of Fire
Sep 24, 2008
4,644
NNJ
I just went through this with my 290. I ordered a rebuilt walbro carb. Didn't want to screw around with rebuilding myself. Runs great now.