Stihl MS290 starts and dies

[Peter Dordal]

My MS290 starts briefly, but dies in seconds. After 2-4 yanks at full choke, it catches a little like it's supposed to. Then, on the next yank at half choke, it seems to start, but dies in seconds, before I can release the choke. It used to run fine; this is a sudden-onset problem.

The spark is strong. I replaced the magneto and ignition wire a year ago, along with the spark plug.
The muffler was replaced 1.5 years ago. It's clear.
I've put in a new carburetor, new fuel hose and filter, new air filter, and new impulse hose.
The compression is around 130-135. There is no visual evidence of scoring on the piston.
The fuel is fresh MotoMix (changed with the new carburetor).

I am completely baffled; up until when this problem first appeared, the saw has started just as it did the day I bought it (outside of a few periods when it's needed simple repairs).

Could the crankcase have a leak? I can see how that might mean the impulse hose had less pressure, and so the fuel pump/diaphragm had less pressure. But at the moment that's grasping at straws.

 

[pioneerguy600]

It is running out of fuel, you need to work on the fuel delivery system and a new carb does not mean its a good working carb.

 

[Peter Dordal]

It is running out of fuel, you need to work on the fuel delivery system and a new carb does not mean its a good working carb.

I didn't spell this out earlier, but this is actually the second carb I've put in to address this problem. The first, a HIPA, I was very inexpensive and I was quite suspicious from the beginning.

Anyway, after I read your comment I went out and looked very carefully at the fuel system, and, sure enough, the fuel line has a sharp kink! That replacement hose I put in came along with the HIPA carburetor, and is very soft. After repositioning the hose, the saw ran for ~1 minute before the hose collapsed again. I've ordered a new hose, hopefully a better one.

All this makes me think I now have a different problem from when I started, but with the same symptoms. I'd left fuel in the tank last fall, and last March replaced the Walbro carb with the HIPA. Maybe the HIPA carb was not a good one, but it now seems that the fuel line I replaced at the same time -- just because it seemed like it would be a good idea -- was definitely bad. Last week I replaced the HIPA carb with a better one, but the saw still didn't start; that's when I posted here.

Thanks for your suggestions!

 

[dswensen]

I didn't spell this out earlier, but this is actually the second carb I've put in to address this problem. The first, a HIPA, I was very inexpensive and I was quite suspicious from the beginning.

Anyway, after I read your comment I went out and looked very carefully at the fuel system, and, sure enough, the fuel line has a sharp kink! That replacement hose I put in came along with the HIPA carburetor, and is very soft. After repositioning the hose, the saw ran for ~1 minute before the hose collapsed again. I've ordered a new hose, hopefully a better one.

All this makes me think I now have a different problem from when I started, but with the same symptoms. I'd left fuel in the tank last fall, and last March replaced the Walbro carb with the HIPA. Maybe the HIPA carb was not a good one, but it now seems that the fuel line I replaced at the same time -- just because it seemed like it would be a good idea -- was definitely bad. Last week I replaced the HIPA carb with a better one, but the saw still didn't start; that's when I posted here.

Thanks for your suggestions!

You might check your tank vent as well. A plugged vent might be allowing for a lowering of the pressure in the tank as fuel is drawn out of it. That would make a soft fuel line problem worse.

 

[HarleyT]

Go to the Stihl dealer and buy the fuel line......

 

[cuinrearview]

Those pre-molded Stihl fuel lines are not a place that you want to cheap out.

 

[Peter Dordal]

Ok, I went to the dealer and got the fuel line. The dies-after-starting problem is still there. So it's one of these three:

1. I have three bad carbs in the shop: the original (which is a Walbro), the HIPA, and the one from "procompany".
   
2. I have three carbs with bad L/H/LA settings (probably only the HIPA and procompany; the Walbro presumably is gummed up inside as I left the saw with fuel in it early last fall). But I haven't tampered with these settings.
   
3. It's something else entirely

Are bad online carbs that much of a thing? I'd be happy to spend the money at the dealer to get a Walbro, but at this point I'm not certain that would do it. Is it actually true that a gummed-up carb can't be cleaned? If not, maybe I should try that. I don't think it's the tank vent, because I've been keeping the tank only half full with fuel.

 

[cuinrearview]

Two aftermarket and one old carb all being bad is possible, but if the symptoms are identical I would question it. Re-set each one to the settings on the cover where the adjustment holes are.

After it dies if you loosen the fuel cap can you hear air moving?

 

[HarleyT]

1127 120 0604 CARBURETOR HD18A $34.01


1127 120 0605 CARBURETOR HD21A $34.01

 

[dswensen]

Two aftermarket and one old carb all being bad is possible, but if the symptoms are identical I would question it. Re-set each one to the settings on the cover where the adjustment holes are.

After it dies if you loosen the fuel cap can you hear air moving?

I still think it could be a tank vent problem. OP, how many seconds after starting does it die? 1 second? 30 seconds?

 

[Sam R]

I don't think a bad tank vent would keep it from running that quickly. It takes it awhile to build up enough vacuum to where it can't pull any more fuel. I think it's something to rule out though; those 290s I believe had the old grub-screw type vents, didn't they? Easy enough to sort out.

How is your air filter, and since you've put a new carb on it - did you change from the old style carb to the new, i.e from non-compensated to compensated. If you didn't also change over your air filter the plate on the old filter will blockade the compensator port and you'll get no or very little atmospheric equalization.

 

[a. palmer jr.]

How about your impulse hose? I had a similar problem to yours on my 361 and it turned out to be a leaky impulse hose...

 

[Wood Doctor]

How about your impulse hose? I had a similar problem to yours on my 361 and it turned out to be a leaky impulse hose...

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.

 

[sb47]

Mine did that and it was the plug that was the problem. I know you said you put in a new one some time ago, but try a new one anyway.

 

[Wood Doctor]

Mine did that and it was the plug that was the problem. I know you said you put in a new one some time ago, but try a new one anyway.

And, it's a lot easier to change the plug than the crank seals -- maybe the understatement of the year. However, I seldom run into bad new plugs or even bad old plugs for that matter. Spark plugs tend to last and last...

 

[sb47]

And, it's a lot easier to change the plug than the crank seals -- maybe the understatement of the year. However, I seldom run into bad new plugs or even bad old plugs for that matter. Spark plugs tend to last and last...

Yeah but a plug is easy and cheap to try.

 

[cus_deluxe]

not long ago i had 2 out of 3 brand new ngks not work. as said above, aftermarket lines for stihls are not something to mess with.

 

[a. palmer jr.]

Rather than change the seals why not do a pressure test to make sure it's leaking before going to all that work. Might be something wrong with the carb, etc.. Those 1127s are easy saws to do a pressure test on..

 

[Peter Dordal]

Two aftermarket and one old carb all being bad is possible, but if the symptoms are identical I would question it. Re-set each one to the settings on the cover where the adjustment holes are.

After it dies if you loosen the fuel cap can you hear air moving?

I've reset the H/L screws based on 1.25 turns out from fully closed. Also 1.0 and 1.5 turns. Nothing matters.
I've tried starting the saw with the fuel cap cracked. That doesn't help either. But, as the tank was not close to full, I don't think there's enough time for a significant pressure change to develop.
The saw dies within 1-5 seconds of catching on the 1/2-choke setting. Not much fuel is drawn out of the tank in that interval.

 

[cuinrearview]

Will it run longer on a little mix dribbled into the cylinder through the plug hole or into the carb throat? If so there's your answer.