Stihl MS290 starts and dies

[Peter Dordal]

I think he changed out the impulse hose. However, I tend to lean toward bad crank shaft seals. I had an 025 do the same thing a few years back -- start and then die like a fly. New seals fixed the problem. It only takes one of them to go bad, but both should be replaced if you make the effort.

I'm re-reading my shop manual, and I'm inclined to agree that this is worth pursuing. Bad seals mean that the impulse hose doesn't do much, which in turn means that the fuel pump doesn't do much.

But checking this requires special seals for the muffler and carburetor. So this is moving slowly.

 

[cuinrearview]

I'm re-reading my shop manual, and I'm inclined to agree that this is worth pursuing. Bad seals mean that the impulse hose doesn't do much, which in turn means that the fuel pump doesn't do much.

But checking this requires special seals for the muffler and carburetor. So this is moving slowly.

Nah, get creative with some bicycle tire tube.

 

[Wood Doctor]

Nah, get creative with some bicycle tire tube.

Actually, I'm trying to figure out what "special seals" for the muffle and carb that OP is talking about. I've rebuilt both a 310 and a 290 by adding a 390 top end yo each and I never saw any special seals. The problem is that replacing the seals usual requires a major take down, even though the service manual says you can do it without removing the cylinder. That to me is next to impossible. You have to be able to lift the cylnder up.

 

[pioneerguy600]

Actually, I'm trying to figure out what "special seals" for the muffle and carb that OP is talking about. I've rebuilt both a 310 and a 290 by adding a 390 top end yo each and I never saw any special seals. The problem is that replacing the seals usual requires a major take down, even though the service manual says you can do it without removing the cylinder. That to me is next to impossible. You have to be able to lift the cylnder up.

To do a Vac and pressure test.

 

[a. palmer jr.]

Just requires a piece of inner tube to go between the muffler and the engine and a rubber cork to stop up the intake with the carb off. Pump some air into the impulse hose and see if it holds around 6 lbs of pressure. I use a blood pressure bulb and some small rubber hose coupled to a gauge with a T fitting. You can always use a little liquid soap and water to help find the leak if any...

 

[Peter Dordal]

Well, finally, after splurging on a genuine Stihl/Walbro carb and finding that made no difference whatsoever, I gave up on repairing it myself.

I took the saw in to my Stihl dealer on Monday.

They called back this morning, to say it was fixed! Ran great!

And all they did was adjust the magneto gap.

From a technical standpoint of fuel+spark+compression=runs, I guess it was the spark. But not only had the saw run more or less fine for those 1-3 seconds each time I'd try it, but I'd checked the spark with my spark tester (multiple times). I gather that the spark tester is useless at distinguishing between a weak spark and a good one, but I had no idea a small gas engine could consistently run-and-die due to a weak spark. I have always believed that if the spark is too weak to stay running, then it's too weak to start.

Guess not. Live and learn.

I had replaced the magneto a year ago, due to an outright broken ignition wire, and I did at the time have trouble setting the gap. But in the end I'd believed I'd gotten it right, and the saw ran fine then. And I can't imagine that vibration since then would enlarge the gap; that magnet has a lot of force.

So it was not a crankcase leak, or low impulse-line pressure, or a maladjusted carb, or bad rings, or cylinder scoring, or any of those weird things.

I picked it up this afternoon. $35.

 

[Wood Doctor]

Coil gap between the IM and the flywheel should be about 0.01". Not sure how yours got out of whack. I suppose it could happen with use. I use an old feeler gauge to set the gap and some just use a common business card.

Never ceases to amaze me at how many engine problems are electrical. Thank you for posting this, but I must admit that I never suspected the coil gap to be the problem. If that occurs, usually the saw will not start at all and no spark will exist.

I fixed my Husqvarna 353 yesterday with identical synptoms that you presented in post #1 by replacing the carb. It runs perfectly today. Gasp!