Stihl MS 290 stalls and won't restart

[iiYolunda]

Hey everyone, my first post here, so I have a MS 290 that stalls after around 5 minutes of running and no matter what will not restart until it cools down again.

So some info about the saw, I've been rebuilding it for a friends friend who brought it to someone (a dealer I guess) and was told to it wasn't worth fixing so he brought it to me to look at since I have some knowledge about small engines and a Youtube degree lol. Well anyway, had low compression so I peaked in the exhaust and piston was scored. Being the nice friend I am, lol, I told him I can rebuild it for him and he'll just have to pay for parts to make the saw like new again...

Disassembling was easy minus those rubber grommets for the Anti-vibration that holds the top plastic cover in place, so got the parts in the mail and got to work. So to make things easy I've bought the top end assembled already with the crankcase, used some high temp silicone sealant for the halves and put everything back together. Alongside with the whole engine, I've also replaced some parts that I'd think would wear down after time : Ignition Coil, Carburetor (to lazy to rebuild), Fuel filter, Air filter, Sparkplug, 20'' Bar and Chain. I've inspected all the hoses including, impulse line, fuel line, and I guess the intake boot and they all were in good shape with no cracks.

Well after finishing the puzzle of reassembly, I go to start the thing and it did take a while as I kept flooding it. Was using 32:1 fuel mixture to break in the thing, and it was a smoke machine, neighbors siding is still blue, lol. So I rev it up a bit, everything seems normal, idles ok, but sometimes it does race a bit and then go back down. After around 5 mins of running (idling) it shuts off and won't restart until it's cold again. I've tried a combination of things such as checking the fuel vent line, which is clear. Also I know it's getting fuel because I can smell it plus the plug is wet, and I also know it's still getting spark when cold and also when hot (got the burns to prove it). Over the course of like the last 4 days, I've been trying to get it running and like I said starts fine when cold, but after running for a bit it dies and won't start back up no matter what you do. I've got it all apart again on my bench looking for maybe an air leak and been going through everything. All and all, the total amount I have into the saw is $210 including the free labor. Anyway now I know next time not to fix things for a friend... who knew a 6x6 box could cause such headaches...

So once again some of the things I've checked, impulse line for cracks (none), fuel vent hose (clear), always has spark when either hot or cold, has compression of course, tried 2 different spark plugs (gapped at .020''), seems to be getting fuel, plus I'm sure there's some other things I can't think of right now. I don't have a tool to pressure test anything otherwise I would of played around with that. I've been able to get around 2 tanks of fuel ran through so far between my cold starts, and have since switched to 40:1 fuel still with the same problem.

Alright so does anyone have any idea's of what could be causing this? Sorry about my short novel lol, thanks in advance.

 

[RedOctobyr]

We know you just need fuel, compression, and spark (at the right time). From what you're seeing, you have all 3. So there is something that we're missing.

Things I would try, if it were me:
- After it dies, pull the air filter, splash a little mixed fuel into the carb throat, and try starting it. This should make sure you're providing fuel, even if the carb is having trouble.
- Do you have an inline spark tester? The kind that you put between the spark plug boot, and the plug, that flash when the plug fires. If so, I'd put that inline, and run the saw with it installed. You should see it flashing the whole time while it's running. When the saw stalls, is the tester still flashing? If so, you still have spark when it's dying. This would eliminate needing to mess with the plug wire to check for spark visually on the spark plug. Perhaps something weird is happening, like losing contact in the plug wire (like at the coil or at the plug boot) while running, then re-establishing a connection when pulling the plug wire off? Admittedly, this is a stretch, but being able to monitor the spark right when the saw dies might tell you something. My tester was about $5 at Harbor Freight.

How does it stall? Does it, say, slowly falter and die, like you ran out of gas? Or does it just die suddenly, like if you switched the saw off? If it dies slowly, if you give it partial choke when it starts to die, does it keep going longer?

You still have good compression after it dies, presumably?

What if you disconnect the kill switch? Perhaps it's grounding out somewhere after a while when the saw is running? You could presumably still shut the saw down by turning the choke on, even without the kill switch.

 

[Roll Tide]

Is the sealent you used fuel resistant, most are not unless it states that it is. Sounds like an air leak could be happening after the sawis warm.

 

[iiYolunda]

Thanks for the responses guys,

@RedOctobyr , Once I get the saw back together I'll definitely try splashing some fuel into the carb after it does it's stalling thing. I do also have an inline spark tester I'll hook up to it and watch what happens, and with the stalling it stalls just like I hit the off switch. It could be idling perfectly with no hesitation and then it just dies. Yes the compression still feels good once its hot. Thanks for some ideas to try tomorrow.

@Roll Tide , this is the sealant I used : http://www.amazon.com/Pro-Seal-80726-Hi-Temp-Silicone/dp/B000FW7VNW

Yeah, I'm also thinking an air leak somewhere, that's why I re-re-tore down to double check everything again. Was there a certain way I was supposed to do the sealant? I just fairly spread some around on the crankcase half, I didn't do around the circle indented area (where the seals contact), and just put the other half in and tightened up, some small amount of it squeezed out around the sides. Was there some other way like snugging it up and letting it dry first and then tightening or something? Anyway thanks for the post.

 

[cali6construction9]

Check the fuel cap or even leave it off if it doesn't die the breather holes in the cap are clogged Poulan chainsaws are bad about that I've had the problem with a craftsman 20hp mower to

stihl 026 husky 300xp mac 610 efco 132s craftsman 170 mac 1635

 

[RedOctobyr]

Good point! If you can't run it with the cap removed, then at least run it until it dies. Then remove the gas cap completely, and reinstall it. This will eliminate any vacuum in the gas tank, if that's the problem (if the tank isn't venting properly). Then try to re-start it. If it's suddenly fine for another 5 minutes, then the odds are excellent that you're drawing a vacuum in the tank, due to a venting problem.

 

[Cope1024]

The silicone sealer you bought doesn't say fuel resistant. Also, with all the money you spent on parts, I would have replaced the impulse line and fuel hoses as well. Good luck with the problem.

 

[iiYolunda]

@cali6construction9 , The fuel caps don't seem to have any sort of vent holes on it, ill definitely take a better look though. It also does make a whoosh like 3 out of 4 times when you open the cap after it's been running, also when I took the carb off to clean it again and removed the fuel line, like a 1/4 of the tank squirt on me. I'll try leaving the cap open or leaving the fuel tank vent hose off when it's running next time. Thanks.

@Cope1024 , Your right, I guess when I did it I didn't read everything on the back, says "Not recommended for constant immersion in gasoline". Whoops lol, then what good is it for if it's hi-temp and for auto use? Well anyway I've got some other Dap Gasket Maker that can handle 400 degrees, I'm pretty sure it said fuel resistant on the cardboard it came in that I threw out. I'll separate the two again and cut off the old stuff and put the other maker I have. I'll put everything back together and let it cure overnight and let you all know how it runs tomorrow. I know I should have replaced the hoses since I already did basically half of the whole chainsaw lol. I did stretch them every way possible and there's no cracks and rubber is still flexible. I guess replacing those will be my next plan if it still don't run right. Thanks.

 

[cali6construction9]

New style cap the flip up wing nut style.. if so I believe they can be popped apart I haven't had my hands on one in years though

stihl 026 husky 300xp mac 610 efco 132s craftsman 170 mac 1635

 

[lone wolf]

Hondabond or Yamabond will both work.

 

[cali6construction9]

A whoosh like a vacuum all of a sudden sucking air into the tank kinda like when you pop the top off a hot gas jug..

stihl 026 husky 300xp mac 610 efco 132s craftsman 170 mac 1635

 

[RedOctobyr]

There is a tank vent, I assumed that vent allowed air in, not out. If that's true, wouldn't the vent be the suspect, not the cap?

Sent using Tapatalk.

 

[cali6construction9]

They're both suspect as far as I believe all caps are vented but yeah that's the problem if the lines good It'd have to be the cap

stihl 026 husky 300xp mac 610 efco 132s craftsman 170 mac 1635

 

[iiYolunda]

Okay, got some good news. So I got the saw back together for the 3rd time now, put some gas in it, fired right up and got my chair to watch it.. so I ended up sitting there for 30 mins till the saw idled empty. Refilled it, fired up first pull and runs great. Tuned it up so it puffs a little when you give it full throttle and all looks good. Let it cool down fires up easily and runs like all my other Stihls.

So I guess not using the right silicone in it caused an air leak that would affect it once it gets hot. Also some other things I changed, inspected the impulse line again and found it did have a small crack in it and was loose on the carb fitting. Instead of waiting on parts again I had some new fuel line laying around and it ended up fitting perfect. Got the guy picking the saw up tomorrow and glad to get finally rid of this thing. I hope I never see it again lol.

Some final words... don't ever tell a friend you'll rebuild their chainsaw and not charge them labor... I've remembered every screw on this thing... lastly, make sure you read the back of the sealant you use and make sure it does not say "not recommended for constant immersion in gasoline." Lol. Once again thanks everyone for the help

 

[Wood Doctor]

If that gasket seal between the carb and the intake manifold boot leaks, it will produce results just like this on about every odd-numbered Stihl saw that exists--o25, 029, 031, 039, etc. Looks like the 290 is not immune from it either.

 

[RedOctobyr]

I'm glad you got it figured out! Thanks for sharing the findings.