Need Help with MS290 bogging

[TheNatural]

I have a Stihl MS 290 that is not running well. I bought it used years ago, used it a very little bit over that time, and couldn't get it going well when I took it out this year.

It's always been a bit tough to get started and that continues (from what I've found online it's just the way they are), but new issue is: whenever I try to rev it, it bogs down and dies. No amount of adjustment in the H screw on the carb made any difference.

I replaced the carb, air filter, fuel filter, fuel line, and spark plug. Cleaned spark arrester screen and used a propane torch to burn off a small amount of gunk in the muffler. Tuned new carb idle and L no trouble. It idles fine once I get it going (just like it did before all of this). None of the parts I replaced or cleaned seemed bad at all. Fuel is fresh Stihl branded premix that runs great in my string trimmer. It's still bogging down under any throttle.

What am I missing?

 

[hacskaroly]

Hello and welcome to the forum!! You have gone through the steps I would have, frustrating that you have not found the issue after replacing the parts you did. At this point I would think that you might possibly have an air leak somewhere (oil seals, carb mount, base of cylinder). If you have some non flammable brake cleaner, start your chainsaw, let it idle and then spray some brake cleaner around where the carb mounts to the cylinder, if there is a leak here, it will suck in the brake cleaner and stop the saw (briefly breaks the combustion cycle - no damage to the saw). If the saw continues to idle, try spraying around the flywheel side oil seal and then around the clutch side. If there are any leaks, the saw will stop running and you will have narrowed down where you need to look.

I found this video helpful, might have some information that will help you:

Good luck with the troubleshooting and let us know if you find anything new!

 

[Czed]

I have a Stihl MS 290 that is not running well. I bought it used years ago, used it a very little bit over that time, and couldn't get it going well when I took it out this year.

It's always been a bit tough to get started and that continues (from what I've found online it's just the way they are), but new issue is: whenever I try to rev it, it bogs down and dies. No amount of adjustment in the H screw on the carb made any difference.

I replaced the carb, air filter, fuel filter, fuel line, and spark plug. Cleaned spark arrester screen and used a propane torch to burn off a small amount of gunk in the muffler. Tuned new carb idle and L no trouble. It idles fine once I get it going (just like it did before all of this). None of the parts I replaced or cleaned seemed bad at all. Fuel is fresh Stihl branded premix that runs great in my string trimmer. It's still bogging down under any throttle.

What am I missing?

Low compression will make them hard to start
If compression is good google muffler mod stihl ms290 it helps those to start easier and a bit more power as well
You have to retune it after s muffler mod.

 

[Brad Button]

Do a leak-down test to see if you have an intake leak.

 

[beaglebriar]

I have a Stihl MS 290 that is not running well. I bought it used years ago, used it a very little bit over that time, and couldn't get it going well when I took it out this year.

It's always been a bit tough to get started and that continues (from what I've found online it's just the way they are), but new issue is: whenever I try to rev it, it bogs down and dies. No amount of adjustment in the H screw on the carb made any difference.

I replaced the carb, air filter, fuel filter, fuel line, and spark plug. Cleaned spark arrester screen and used a propane torch to burn off a small amount of gunk in the muffler. Tuned new carb idle and L no trouble. It idles fine once I get it going (just like it did before all of this). None of the parts I replaced or cleaned seemed bad at all. Fuel is fresh Stihl branded premix that runs great in my string trimmer. It's still bogging down under any throttle.

What am I missing?

Typically these are no harder to start than any other saw. Pull the muffler and check for scoring before going any further.

 

[TheNatural]

Hello and welcome to the forum!! You have gone through the steps I would have, frustrating that you have not found the issue after replacing the parts you did. At this point I would think that you might possibly have an air leak somewhere (oil seals, carb mount, base of cylinder). If you have some non flammable brake cleaner, start your chainsaw, let it idle and then spray some brake cleaner around where the carb mounts to the cylinder, if there is a leak here, it will suck in the brake cleaner and stop the saw (briefly breaks the combustion cycle - no damage to the saw). If the saw continues to idle, try spraying around the flywheel side oil seal and then around the clutch side. If there are any leaks, the saw will stop running and you will have narrowed down where you need to look.

I found this video helpful, might have some information that will help you:

Good luck with the troubleshooting and let us know if you find anything new!

I'll give this a try next. Thanks.

The video was good. It sounds like a lean bog, but has persisted with the H screw backed way out. You got me thinking about it though, and a significant air leak makes sense.

Is there anything in the brake mechanism that could be dragging/sticking/corroded causing me some grief? The clutch engages and chain spins with brake off, but doesn't manage to build up any real speed before bogging. I only ask because that's the area of the saw I know the least about... Not because I have any reason to suspect an issue there.

 

[hacskaroly]

Is there anything in the brake mechanism that could be dragging/sticking/corroded causing me some grief? The clutch engages and chain spins with brake off, but doesn't manage to build up any real speed before bogging. I only ask because that's the area of the saw I know the least about... Not because I have any reason to suspect an issue there.

I don't believe the brake mechanism would cause this. With the saw off, if you release the chain brake (off) and can freely move the chain (use a scrench behind a cutter) then that would tell me there is nothing wrong there or nothing that could potentially cause bogging issues. Typically with saws, you can have the chain brake on and run the saw full throttle (not recommended) and it won't bog like you are describing. That is why I don't think it is the brake mechanism. I think like said above, check the piston for scorring (remove the muffer and look) and do a leak-down test to see if you have an air leak.

Just from the description it sounds like the saw is getting the right amount of fuel and air to idle, however when you start to rev it, its wanting to pull in more air while it is squirting in more fuel and since the carb only lets in so much air the suction is pulling more air in from somewhere else creating a larger air-to-fuel ratio, off balance to the point where it cannot properly combust and you get the bogging.

 

[TheNatural]

I think like said above, check the piston for scorring (remove the muffer and look) and do a leak-down test to see if you have an air leak.

Just from the description it sounds like the saw is getting the right amount of fuel and air to idle, however when you start to rev it, its wanting to pull in more air while it is squirting in more fuel and since the carb only lets in so much air the suction is pulling more air in from somewhere else creating a larger air-to-fuel ratio, off balance to the point where it cannot properly combust and you get the bogging.

I do not have any non flammable brake cleaner on the shelf, but it didn't want to start for me just now anyway. I checked the piston and cylinder and both look good to me. No scoring.



I had a closer look at the clutch and although it looks a bit rusty, it spins freely with the saw off as it should and everything seems to work properly. The plastic around it looks burnt. If it got hot enough to melt this plastic, would the seal behind it also melt? I did not pull the clutch off (no piston stopper on the shelf either).



I also pulled the cover/pull starter off the flywheel side, but did not pull the flywheel. I couldn't see much from that angle, other than the jug seems to have an awful lot of oil on it everywhere.

Typically these are no harder to start than any other saw. Pull the muffler and check for scoring before going any further.

Maybe my difficulty starting it was an early symptom of an air leak?

 

[hacskaroly]

No scoring.

I had a closer look at the clutch and although it looks a bit rusty, it spins freely with the saw off as it should and everything seems to work properly. The plastic around it looks burnt. If it got hot enough to melt this plastic, would the seal behind it also melt?

I also pulled the cover/pull starter off the flywheel side, but did not pull the flywheel. I couldn't see much from that angle, other than the jug seems to have an awful lot of oil on it everywhere.

Good to see that it isn't scored. As for the oil all over, its a good idea to clean off what you can, any build up around the cylinder hinders heat dissipation and too much can lead to overheating and scoring.

In regards to the clutch, I have two MS 271s with that issue that can be caused by either hitting the brake unintentionally while running full bore (and keeping going) or too much wood chips, saw dust and oil packing in back there pushing the break spring against the clutch while it is spinning, creating lots of heat and melting plastic. I think the rust color on the clutch is indicative of it getting really hot from that. It is very possible that the oil seal on that side is compromised. If you can remove the clutch and the oil worm gear, you should be able to inspect the oil seal. If you don't have a piston stop, you can use a rope, I use a nylon braided rope to stop my pistons.

With that burn damage I would recommend getting in there doing a full inspection to make sure everything is good to go. As for my 271s, I had to take a dremel and grind down melted plastic, but will probably end up getting a new case ($30-40) on eBay that does not have that damage. My dad had one of the 271s and it failed twice, I think the second time was from the melted case that pushed the brake spring against the clutch continuously.

 

[hacskaroly]

For your reference, here is what my MS 271 looks like (albeit the clutch is a new one, the heat jacked up the springs on the old one and they lost their spring).

1. Either the chain break was hit while under full throttle and kept going or crap got wedged between the brake spring and body causing constant friction of the chain brake against the clutch causing excessive heat build up. Melted plastic was the small stuff, caused needle bearing to disintegrate.


2. The rope I use as a piston stop. I remelt the end as needed and cut it and start new when it gets too rough.


3. With the clutch pulled you can see the melted plastic damage, it was extensive and I had to dremel out what I could to keep the brake spring from pushing against the clutch because of it. The oiler is new, the other one melted. I cleaned all of the dirt and debris out of there, what you see is all melted and charred plastic. I will probably get another case off of eBay and pitch this one, I could make it work, but I don't want to chance cleaning up the plastic and weakening it any further. The saw runs fine.


I saw a rash of these (271s) at work two years ago that came in with this problem, I think they all happened with crap getting behind the plastic and between the chainbrake spring and the body. Its what make the most sense from the people that described what they were doing.

 

[lehman live edge slab]

I’d say this saw has an air leak, it has always had a small one since you got it because of the hard starting in my opinion. Without a good seal on case you have low vacuum impulse for the carb to suck fuel. This his now gotten a leak that the jets on carb can supply enough fuel at idle only and anything above it leans out and bogs. Vacuum and pressure test saw I’m sure it needs crank seals, but if for some reason it passes the tests you may have gotten a bad new carb it aftermarket cheapo. They make 2 different sets of crank seals for these saws one type has a heavy wire clip in them and are a drive in style seal the others are a regular style and require the saw to be disassembled. I usually use the standard cheaper one so I can inspect the whole saw when I pull it down.