Stihl ms291 acting up

[Team4LongGun]

Very new, not much use on it. Once it gets warmed up, it starts acting crappy. Hard to keep running, bogs, have to stay on throttle well past cut.
Is there a carb adjustment? It did come from back east, and I am at 3500'. Not sure if this would be it?

Local repair is pricey, just for taking it in.

TIA

 

[COelk89]

Youtube for precise instructions, yes there are carb adjustment(s) on the bar side. Also some stihls have a little air blocker to put in during winter to run richer I believe.

 

[Billdoe]

Is the spark arrestor clean? Pull it and check along with air filter and plug

 

[Hoodie]

I work from 900ft above sea level up to about 4000ft and have definitely had to make adjustments with that degree of elevation change.

Assuming air filter is clean, that's where I'd start. If it's new with not much use spark plug and spark arrestor are likely fine.

 

[RockAndSage]

The first thought that came to mind was what kind of fuel it has in it, and how long that fuel has been in it.

The canned pre-mix fuels, left in a small motor over a season or two, seem to be causing more than a few tools to get a bit gummed up in the fuel system.

 

[Marbles]

There is a carb adjustment, check the air filter and fuel filters.

Not particularly helpful for the OP, but my experience with Stihl is their Pro line is great (MS261 is the MS291's adult brother), but the Farm and Ranch and Home Owner lines are not woth paying for (I've had better luck with Husqvarna for the cheaper stuff).

 

[Team4LongGun]

The first thought that came to mind was what kind of fuel it has in it, and how long that fuel has been in it.

The canned pre-mix fuels, left in a small motor over a season or two, seem to be causing more than a few tools to get a bit gummed up in the fuel system.

I only do non ethanol that I pre mix myself

 

[Nickofthewoods]

I seem to recall having similar issues on my 261 before and I think I determined it was old fuel that I just dumped out and it ran fine again. Maybe @Marbles is right though because I've had my 261 for 12 years and it has been very reliable with just basic maintenance.

 

[Mighty Mouse]

The fuel line between the tank and carb on my MS251 will get rotten and develop cracks and cause the saw to struggle above idle. I’ve tried OEM and knock-off replacement lines and haven’t found one yet that lasts. I‘ve resolved to just keep a few spares on hand at all times. Different saw and somewhat different symptoms, but worth checking and cheap to fix.

 

[BluMtn]

The fuel line between the tank and carb on my MS251 will get rotten and develop cracks and cause the saw to struggle above idle. I’ve tried OEM and knock-off replacement lines and haven’t found one yet that lasts. I‘ve resolved to just keep a few spares on hand at all times. Different saw and somewhat different symptoms, but worth checking and cheap to fix.

Ethanal gas will tear those gas lines up. When I was an Ag service manager we sold Stihl saws. My saw guy had a box of those fuel lines on his bench. When a poorly running saw came in he would change that fuel line and 95% time it would fix the problem.

 

[Mighty Mouse]

SheugEthanal gas will tear those gas lines up. When I was an Ag service manager we sold Stihl saws. My saw guy had a box of those fuel lines on his bench. When a poorly running saw came in he would change that fuel line and 95% time it would fix the problem.

I only run non-ethanol fuel in my saw (and only use Stihl fuel oil FWIW). Fuel line still rots in a matter of months

 

[BluMtn]

Interesting, my Stihl is 14 years old and still has the original fuel line in it. I use non-ethanal with seafoam.

 

[mxgsfmdpx]

There’s a reason all the arborists say homeowners buy Stihl and they all buy Husqvarna

 

[mxgsfmdpx]

I’ve had to lean mine out a bit when going from 1,500 feet at home to 5,500 feet at our old cabin.

 

[Sunshine40]

Not saying it's it but I've seen it happen before, is your bar oiling properly? I've seen oil ports get clogged on saws therefore starving the bar of oil and creating friction and pinching the chain in the sliders. Sometimes it's just saw dust packed in there choking it and can be cleaned pretty easily.

Stihl tunes and runs all of their units at the factory so very rarely is a carb adjustment the fix to a problem. If a carb adjustment does fix it it's probably compensating for something else that's wrong. Also 3500' isn't an altitude where you should be seeing massive power fall off. That's usually a 6-8k thing.

Check to see if the fuel is bad, spark gap, and pull the starter cover and see if your coil is gapped properly.

The only other thing I could see is your saw may have sat somewhere for a while before you bought itand the diaphragms in the carb got dry. I only saw this less the a dozen times when I worked for Stihl and it was usually on crappy 170 saws but it isn't something to rule out.

It's hard to diagnose without seeing it but just tryin to throw out some ideas out of the norm that I saw while I worked for Stihl and felt with peoples problems every day.

 

[Marbles]

There’s a reason all the arborists say homeowners buy Stihl and they all buy Husqvarna

I know professionals that use Stihl, and Husqvarna. Stihl's Pro line has been phenomenal for me, the 201T needed a lot of break in, use that sucker on the ground for 100 or so hours before taking it up a tree, it is a nice saw once broken in, but I've heard of the "accidentally" going into the chipper when new.

When I get a big saw, it may well be a Husqvarna. I'm too busy spending my money on mufflers and scopes to get one at the moment as my saws rarely get used at present.

 

[TaperPin]

Very new, not much use on it. Once it gets warmed up, it starts acting crappy. Hard to keep running, bogs, have to stay on throttle well past cut.
Is there a carb adjustment? It did come from back east, and I am at 3500'. Not sure if this would be it?

Local repair is pricey, just for taking it in.

TIA

Lean running can be air leaks, as well as fuel issues. Check for loose carb and jug bolts first, then a quick check for air leaks at the jug gasket and carb to jug, can be spraying carb cleaner, brake cleaner, propane from a torch (no flame!), or anything flammable along the gasket surfaces and if the saw changes rpm it’s sucking air there. Much harder to track down are air leaks at the crank seals - that requires taking the saw apart to see the seals, pressurizing the crankcase, and using soapy water and looking for bubbles.

If your fuel lines are clear, look for bubbles in case it’s sucking air. I have seen slivers of fuel line partially blocking fuel flow, that must have been there since it was birthed from the mother ship.

When the saw starts running poorly, crack the fuel cap to let air in then close it - if the saw runs ok for a few minutes then acts up, the tank air inlet valve may not be working.

Look for anything obviously weird with the crankcase impulse air tube coming from the crankcase to carb. I’d take the carb off and look at the gas pumping diaphragm that the crankcase impulse operates, in case it is split.

I have no idea how to work around the sealed idle screws.

Elevation does make a difference, especially if the saw was slightly lean for some reason when it was at lower elevation, and going up just made it even more so.

 

[Customweld]

I would check the impulse line. The carbs on the non pro Stihl's can also be a real pita.

 

[*zap*]

maybe change/clean the plug and the fuel/air filter. Check the primer bulb and lines for cracks.....if it still is an issue get a carb adjustment tool kit and play with that. you can get a new carb, filters and fuel lines for around $20 but the plugs that come with that kit are usually garbage.
figuring this stuff out is usually simple and straight forward, use utube for guidance and do not pay some crazee fee to anyone else to fix this.
get a funnel with a metal screen in it and always use that to fill the gas tank. the crap and crud I find in gas tanks for blowers/trimmers and saws is amazing...
if you were local we could get this done in an hour.

 

[GSPHUNTER]

Clean carb. ports. See what that does. Just running carb cleaner wont do it.