MS290 won't idle

John Galt

Member
Oct 22, 2019
43
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
4,998
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

Member
Oct 22, 2019
43
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
4,998
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
392
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
4,663
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.
 

John Galt

Member
Oct 22, 2019
43
W Montana
The new carb finally came in and I found a rainy day and five minutes to install it. Fired it up and it ran fine, all the adjustment screws were completely out of wack but it was running. Time for a beer.
I decided to get a tach for peace of mind and since I have no idea what the "burble" sounds like when running FOT so that took another week. I started it up to do the tuning and was getting the low end close when it died on me. Tried to start it again and it got compression locked(?) the stater rope was out and the rotor wouldn't move. I was thinking engine rebuild. It cooled down and unlocked so I tried again and got it dialed in pretty good. Idle is correct rpm, high is a 1000 low. Maybe I'll tweak that later, I was just happy it was running. The muffler wasn't tight the first time, any idea if that would cause the issue? Shaft looks good, a few scratches but nothing major. Time for another beer.
 

gzecc

Minister of Fire
Sep 24, 2008
4,663
NNJ
Mine came adjusted when received. I would be sure to adjust when warmed up if possible.
 

gzecc

Minister of Fire
Sep 24, 2008
4,663
NNJ
Change the fuel line and filter? Be sure the fuel line is not kinked where it makes the turn towards the carburetor.
 

Zack R

Feeling the Heat
Sep 27, 2017
392
Sisters, OR
flic.kr
If you haven't replaced the spark plug recently I'd do that as well, then tune the carb again once the engine is warmed up. I like the E3 spark plugs, they are expensive for spark plugs( ~$8) but they do work well.

Running 1000rpm lower than spec on the top end indicates you are a bit rich, which isn't a bad thing necessarily, but it is leaving some power on the table. After some additional fine tuning (very small changes) you should be able to reach the specified max RPM, while at the same time hear just a touch of "burble" when at max RPM unloaded. Bury the saw into some wood and the burble will go away and it should cut nice and strong.

I sometime struggle to hear the burble with hearing protection on but can hear it without hearing protection. I did this once and now trust the tachometer since its painfully loud to run the saw at full throttle without hearing protection. This was 10+ cords ago and the saw is still running strong and hasn't burned up so I'm happy.
 
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John Galt

Member
Oct 22, 2019
43
W Montana
Yeah, I went down the list on replacing stuff. Air filter, plug, fuel filter. I had it torn down and was ready to pull the fuel line and impulse line when I kept reading that it was the carb. $7 for a new Chinesium carb, plug, filters, and another fuel line. It was worth a shot.
I did get everything very clean as I was doing this so that's an upside. Air filter had never been really blown out hard core, just always a light brush off. Spark arrester scrubbed.
30 cords cut without an issue, we'll see how long it goes after I fixed it. I'll replace the cheap stuff with better quality next time unless it makes it another 5 years.

I just ran through a couple of tanks bucking up a pile. Ran great, a little high idle but cut nicely until I hit a dirt covered log. Time to sharpen the chain and tweak the screws just a bit.
 
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