Saw won't stay running......Stihl MS290

[ericm979]

I have also cleaned out the fuel pickup with clean gas and compressed air.

I don't think that works all that well. I'd replace the fuel filter.
For the carb adjustment it's best to start at the factory recommended starting point, usually about 1 turn out on non limited screws. The saw should run at those settings if there's nothing else wrong. If you're way off of the factory settings on an unmodified saw to get it to run there's something wrong.

It sure sounds like a fuel flow problem. Which could be (as already suggested) the tank vent or impulse line. Also the diaphram in the carb could be damaged, a valve damaged, or a passage plugged. Saw carbs internals are tiny and easily damaged.

 

[Redbug]

A new carb can be bought from Ebay for about $20. Chinese knock offs but work like the brand names. I usually keep a spare carb for each saw, (I have 4), and swap out if I have problems. You can buy impulse line kits and all the other replaceable parts cheap, from Ebay as well.

I took a saw to a dealer once and got skinned on the work done and price charged. I learned the hard way. They messed up other parts to fix what was really broken. There is no way I would ever take a saw or weedeater to a dealer to fix. They most likely order carbs for less than $20 and charge $100.

 

[CobyRupert]

I guarantee the problem is either compression, fuel, spark or air.

The problem is usually not enough of one of the first 3 or too much of the last.
If it runs for a few minutes, then goes wacky, don't overlook checking the compression.

 

[Ford850]

Pull the muffler and inspect to be sure its clean and clear. I had a similar issue which turned out to be mud daubers in the muffler.

 

[/pine]

FWIW...The impulse line is what controls the diaphragm in the carb...if there is a slight crack in the impulse line the diaphragm will not pump any fuel.

I have a MS 390 and it was acting similar to what the OP described...the impulse line gets warm and also has a sharp bend...there were some fine cracks at the bend...

Requires some dismantling and removing the carb. but is a simple repair for the mechanically inclined... positioning the new line onto the inner barb fitting requires a bit of fineness...long nose forceps help...

 

[LongueCarabine]

Thanks for the help, everyone. Looks like I will have some things to do this weekend.

 

[eddie48]

First thing I would do is to open the high speed jet about 1/8 turn and see if that helps. Sounds like it is looking for more fuel when it heats up. Also, when you cleaned the carb, did you use a rebuild kit and clean out the low speed orifices under the metal cover (replacement cover comes in the rebuild kit, which is a more complete parts kit than the gasket kit)? Run fine wires through every hole and opening in the carb when cleaning?

 

[LongueCarabine]

First thing I would do is to open the high speed jet about 1/8 turn and see if that helps. Sounds like it is looking for more fuel when it heats up. Also, when you cleaned the carb, did you use a rebuild kit and clean out the low speed orifices under the metal cover (replacement cover comes in the rebuild kit, which is a more complete parts kit than the gasket kit)? Run fine wires through every hole and opening in the carb when cleaning?

I didn't have a kit at the time. Looking on Amazon, I see kits made by HIPA that include all the fuel lines, an air filter and the carburetor for just over $20. Anyone familiar with these? Decent quality?

 

[eddie48]

I haven't had the best results with the aftermarket carbs. Put three of them on a mantis tiller last year before I found one that worked for more than an hour.

 

[s219]

First thing I would do is to open the high speed jet about 1/8 turn and see if that helps. Sounds like it is looking for more fuel when it heats up. Also, when you cleaned the carb, did you use a rebuild kit and clean out the low speed orifices under the metal cover (replacement cover comes in the rebuild kit, which is a more complete parts kit than the gasket kit)? Run fine wires through every hole and opening in the carb when cleaning?

This is good advice, so many saws run different when they warm up a bit. I always tweak my carb tune for a warm saw. If you tuned it stone cold, it is probably off a bit.