Stihl MS290 Hard to pull recoil

[WoodGirl]

My MS290 had develop a condition where at times it is impossible to pull the recoil; as if the saw is locked up. This is when I try to pull fast to start the saw; you can pull the recoil slowly through each compression stage. Taking the plug out the saw pulls normally. I have been given a couple of scenarios of what can cause this issue; timing off, carb spitting too much fuel in the combustion chamber; also that the ignition module could be acting as a magnetic brake. I have tried numerous tests, muffler off, carb loosen (to prevent the pumping action), trying to start the saw with the ignition boot off the plug, etc. I have not come to any conclusions on the saw. I pulled the clutch drum off and the springs etc on the clutch were good. I took the recoil off and it is good. I have not pulled the flywheel as that is more involved but I can do so if I have a puller that will work. I have found that if I pull the recoil several times that it will "loosen up" and then I can pull quickly enough to get the saw running. I got the saw running yesterday and cut some dead dry poplar with the saw. The saw did seem to want to bog down on me and the chain needed sharpening.

A friend keeps insisting that the saw has too much compression on it. I dumped all the fuel from the tank, removed the spark plug, pulled the saw several times and let the saw sit with the fuel cap open and the plug out for approximately 24 hours or more to be sure there was no fuel in the tank or in the carb. I put the plug back in and the saw was still impossible to pull the recoil fast so it could be started. I pulled the recoil several times slowly and got the saw where I could then pull the recoil normally. I used a compression tester and did three tests and each time the compression was approximately 165. My friend said that was too high and that is the problem. I don't agree because that is the compression when I can start the saw; of course when I can't pull the recoil I can't test the compression.

P.S. What is the normal range of compression on a MS290?

 

[RandyBoBandy]

Is there no decomp button?

 

[salecker]

Take a close look at your recoil
I had a saw that i used for firewood no issues one year then partway through the next year it became impossibly to start like yours. The recoil wasn't right it would bind enough to cause what you are describing,i replaced it with a different one and all was good. I have a pile of parts saws.

 

[WoodGirl]

Is there no decomp button?

Not on the 290 but then it is not that hard to pull when normal.

 

[WoodGirl]

Take a close look at your recoil
I had a saw that i used for firewood no issues one year then partway through the next year it became impossibly to start like yours. The recoil wasn't right it would bind enough to cause what you are describing,i replaced it with a different one and all was good. I have a pile of parts saws.

The recoil was replaced with another (Stihl brand) with the easier pull and two pawls over one. However, I guess it could be the problem.

 

[Solarguy3500]

If you end up pulling the flywheel, you might not need a puller.

I'm not familiar with Stihls as all I've had are Husqvarnas, but on my 372 XPW, I was able to loosen the nut that holds the flywheel, but don't remove it. Then, take the cover off the other side of the saw, exposing the clutch. With the flywheel hanging upside down, tap the other end of the shaft on the clutch side gently. On my saw, that and gravity made the flywheel pop off easy with just a few taps.

 

[WoodGirl]

I looked at the saw again today. I managed to get it started and it was running and then died on me; have never had the saw to die on idle before. I went to restart the saw and was able to pull the recoil out and then acted as if it pulled back on me and smacked hard into my hand. I believe the timing is off on the saw and as I was pulling the spark ignited the fuel and thus the smack back on the recoil. I will attempt to inspect to see if the flywheel is off; sometimes the keys will not shear but deform enough to cause the timing to move off a bit but allow the saw to run. I also recall one time when the saw was hard to pull, seeing wisps of smoke from the exhaust. I will report back on what I find when I get the flywheel off.

 

[ericm979]

Kickback pulling the handle out of your hand can happen even with the correct ignition timing. It's from not pulling hard enough.

The extra effort to pull the saw is probably due to carbon build up on the piston crown and combustion chamber. It does not take much to increase the compression. Normally it's not a problem but if it was already difficult to pull it could be.

Unfortunately the only effective way I know to clean it is to take the cylinder off and gently scrape it off with a tool that won't mar the aluminum. Some chemicals can help that process.

Stihl oil is known to deposit carbon. But even the best low ash synthetic oil will deposit some.

 

[WoodGirl]

Some history may be in order. First of all, I heat only with wood in the winter. I cut almost all of my wood; I have been given some wood over the last few years that was cut by others but the mass majority of the wood I burn is cut by me. My primary saw is the MS290; the only other saw I have is a small Echo for limbing. Therefore, in the last five to six years I have been burning wood, I have started the MS290 many many times as you can imagine. I know the saw has develop an issue that did not use to be there; at this time I am between it being a timing issue with the spark or the carb putting too much fuel in the chamber causing basically a type of hydraulic lock. Now, I removed the muffler as I stated and I was able to see the piston and there is no build-up of carbon on the piston. I could use an inspection camera to see about the top of the combustion chamber but I don't think that is necessary.

I would like an idea of normal compression for the saw.

 

[ABMax24]

Sounds to me like a bad crank bearing or gas without oil mixed in.

I'd try fresh fuel/oil mix first, then double check the flywheel key and ignition system. After that I'd be pulling the engine apart to have a look.

To me 165psi compression doesn't sound abnormal. Even if it was too high of compression it would make the saw harder to pull, but not impossible to pull.

 

[WoodGirl]

I'd try fresh fuel/oil mix first,

Yes, yesterday I mixed up fresh fuel being careful to get it at 50:1 using a measuring device in ounces. While the saw was a bit temperamental on being able to pull the recoil, it did start and I did cut some wood. Today was harder but I got the saw to start but it died in idle. Restarting it smacked my hand so hard that I just stopped until I can pull the flywheel. I know the saw well and know this is not normal with the saw since I have started it hundreds of times.

On the bearings; wouldn't I notice bad bearings with the saw running?

 

[ABMax24]

Yes, yesterday I mixed up fresh fuel being careful to get it at 50:1 using a measuring device in ounces. While the saw was a bit temperamental on being able to pull the recoil, it did start and I did cut some wood. Today was harder but I got the saw to start but it died in idle. Restarting it smacked my hand so hard that I just stopped until I can pull the flywheel. I know the saw well and know this is not normal with the saw since I have started it hundreds of times.

On the bearings; wouldn't I notice bad bearings with the saw running?

Yes and no. Depends on which bearing and how bad. You generally won't hear it if that's what you mean. Pull the spark plug and the recoil and slowly rotate the engine by hand it should turn freely and easily, if it becomes stiff at certain points it could be a bearing, in that case likely on one end or the other of the connecting rod.

What makes me think its a bearing is the way it dies at idle, something could be adding extra friction that can't be overcome by the low power output of the engine at idle.

I would check your flywheel first, the symptoms do also fit an ignition issue, particularly the way it kicks back. After that is ruled out I would look into the engine. I've also worked around small engines enough and don't think too much of pulling it apart it the name of diagnostics. Others haven't, so may wish to pursue other diagnostic tests first.

 

[WoodGirl]

I took the nut off the flywheel; haven't pulled the flywheel. It appears that the key is made into the flywheel; is this true? The photo does show a small gap on one side; would this be enough to throw the timing off to the point it would be hard to pull at times and would kick back on me?

 

[ABMax24]

Yes, on your saw the key is cast into the flywheel.

That little gap isn't your issue unfortunately. It might shift timing a degree or two, not near enough to cause your issues.

 

[WoodGirl]

If it isn't timing then that goes back to the carb puking too much fluid into the chamber resulting in increased compression, or something internal to the saw.

 

[ABMax24]

I have a hard time believing it's the carb, if it was dumping that much fuel you'd see it coming out the exhaust, it would likely foul the spark plugs as well so it wouldn't fire.

Does the clutch bearing spin freely?

 

[ABMax24]

Is there any aluminum melted to the spark plug?

 

[ericm979]

That looks normal. It's a cast piece.

Make sure to torque the nut to the spec in the shop manual. The taper is what holds the rotor in place on the shaft. The key is just to locate it. The nut needs to be tight enough to wedge the rotor onto the taper sufficiently hard. Otherwise it will spin and rip the key off.

It does not take much thickness of carbon to raise the compression significantly. Unless the piston crown is showing bare aluminum it's hard to judge the thickness of the carbon visually.

 

[ericm979]

If it isn't timing then that goes back to the carb puking too much fluid into the chamber resulting in increased compression, or something internal to the saw.

Guys will talk about "hydro locking" but it is super rare in practice , especially in two strokes. And usually caused by riding your motorcycle into a stream that is too deep. If you can pull the engine over it's not hydro locked.

If you don't believe me remove the spark plug, turn the engine upside down and pull the the cord. If there is fluid in the crankcase it will come out the plug hole.

 

[WoodGirl]

I have a hard time believing it's the carb, if it was dumping that much fuel you'd see it coming out the exhaust, it would likely foul the spark plugs as well so it wouldn't fire.

Does the clutch bearing spin freely?

Yes, Also, with the plug out, I can freely spin the flywheel by hand. I looked at the piston and bore when I had the muffler off and they look good. I couldn't feel any rough bearings when turning by hand.

 

[WoodGirl]

Is there any aluminum melted to the spark plug?

No, the plug looks OK. I cleaned it the other day.

 

[WoodGirl]

It does not take much thickness of carbon to raise the compression significantly. Unless the piston crown is showing bare aluminum it's hard to judge the thickness of the carbon visually.

But this isn't ALL THE TIME. If it was due to carbon build up then it would be high compression ALL the time. I had the saw started yesterday and it died on me (which is usually doesn't do) and when I went to start it again, it almost broke my hand. The saw dying could have been due to the carb adjustment; I was told the saw was idling too low. Although I used the saw two days ago and it never died on me the whole time.

 

[WoodGirl]

Make sure to torque the nut to the spec in the shop manual. The taper is what holds the rotor in place on the shaft. The key is just to locate it. The nut needs to be tight enough to wedge the rotor onto the taper sufficiently hard. Otherwise it will spin and rip the key off.

Are these the correct torque for the 290?
Torque Specs
kpm Nm
Nut M8x1 Flywheel/crankshaft 2.8 28.0

 

[ABMax24]

Yes, Also, with the plug out, I can freely spin the flywheel by hand. I looked at the piston and bore when I had the muffler off and they look good. I couldn't feel any rough bearings when turning by hand.

Okay.

Have you checked the ignition coil to flywheel gap? Too much or too little gap can affect ignition timing and cause issues like yours.

Problem is I'm having a hard time finding the spec. 0.008" to 0.012" seems to be in the ballpark though.

 

[WoodGirl]

Take a close look at your recoil
I had a saw that i used for firewood no issues one year then partway through the next year it became impossibly to start like yours. The recoil wasn't right it would bind enough to cause what you are describing,i replaced it with a different one and all was good. I have a pile of parts saws.

I had a tech to look at the saw when it first started acting up. It would only do it at odd times. I shipped the saw to him. He couldn't get it to repeat the issue when he had it but he put another recoil on it; a used recoil but he replaced the rope and put in new pawls. It seemed to solve the problem but then it started returning; infrequently at first but now almost a daily issue. I phoned the local Stihl dealer and they wanted $100 for a recoil. That is too much to spend to play a guessing game. I might get one of the cheap China knockoffs and try it. At this point maybe it is the recoil jamming; if the recoil stops moving as I am pulling up, the reaction force would be just as if the recoil handle smacked down into my hand.