Stihl MS290 Stumble/Bog Off Idle

[jrsdws]

My neighbor buddy has this MS290 that has been through h#ll and back a few times. He's cut a ton of firewood with it but sucks about taking care of anything. He was complaining about it starting to stumble and bog off of idle so I convinced him it was time for some simple maintenance. He stopped and got a little kit with a new air filter, spark plug, and fuel filter. We installed of that I talked him into a mild muff mod. I had to defeat the rev limiters afterwards to get it to tune. It idles fine and runs out and cuts fine....noticeably better than before, but I can't tune the stumble out of it.

I'm leaning towards new fuel lines and maybe carb rebuild now.

Any push in the right direction much appreciated.

 

[Canadian farm boy]

Sounds like your on the right track. How's the air filter?

 

[jrsdws]

Brand new at the time of the other maintenance.

 

[Canadian farm boy]

Pressure/vac test yet?

 

[jrsdws]

Noooo.....just air filter, fuel filter, spark plug, muff mod, and rev limiters defeated. Saw tunes fine for high side and idle we just can't get it the low side to tune the hesitation/bog out.

 

[Magic_Man]

Check the impulse line

 

[Canadian farm boy]

Is it possible that the muffler is to open now? I have a ms 260 that does the same sort of thing but I have an 044 carb on it and the muffler is really opened up. I want to try closing up the muffler a bit. I just haven't had a chance yet

 

[fearofpavement]

Have you tried opening the L screw more? Give it a quarter turn to the left and see if it comes off idle better.

 

[SixGun]

Do what they said, check impulse and fuel line, rebuild carb and test run. I have had to change several carbs ,
even after rebuilding , sometimes that stumble doesnt go away. How is compression?

 

[TJ the Chainsaw Mechanic]

Sounds like a carb kit would be the fix....the fuel pump gasket could be stretched causing it to run lean. Had the same problem with a customer's saw.

 

[jrsdws]

I think I'll be getting the saw back today so I'll move on with impulse, fuel line, and carb kit. I'll throw my compression tester on it but it feels okay. What do these normally run?

 

[SixGun]

Compression varies but I would say you want to see around 150. Absolute minimum to be around 120. If the guy was that bad at maintaining his saw, his top end could be tired from dirty air.

 

[Poleman]

I'd try what fearofpavement suggested and richen the L. If that doesn't help it's time to check the other items, impulse line, carb kit, fuel line & filter. If he is poor on maintenance it could be any of those listed.

 

[jrsdws]

Got to play with the 290 a little more tonight after sharpening chains and such. I continued to make fine adjustments to the L screw and it's much better. It was actually a little too rich and loading up with fuel. That carb has the touchiest damn adjustment screws ever.

Oh I checked compression after the saw was partially cooled and got 170psi with my Snap On gauge.

Hopefully we'll cut wood this weekend and see how it does, but I think I'll get the picky little bugger.