How the hell did I kill another Stihl?

[Skunkdynamite]

So I was just overjoyed to get my290 to 390 rebuild up and running, I made a few cuts and gave it some rest.
Fired up the 261 to lay down a few trees on the list and it stalled out on me... Weird.

Thinking about it the last time I ran it, it stalled and seemed a little weaker in the cut.
I bought it on Ebay from the seller with the fancy background... Had pics of it with a compression gauge on it. I repeated the same reading when I got it in the mail. Thought that was a good indication of internal conditions... Upon going over it, she looked a little dirtier than any saw I'd ask $400 for.
Since I got it in September I ran a quart of premix 2 stroke fuel and a tank or two of Ethanol free 91 both mixed at 40:1
Pulled the spark plug every time I ran it to check for conditions too...
It stalled mid cut on me today, just like when my 291 died... Pulled the muffler and the rings are scored and so is the piston. A littlehheavy on the carbon in the exhaust port too... I did zero modifications to this one, wanting the pro saw for the resale value when I got my other saw back together. I really don't know what the problem is here...
Can a beat up saw still have good compression for a few runs? Did I get bamboozled by a seller of junk or am I just killing perfectly good equipment?!


What the hell am I doing wrong?!?!
I've never killed a chainsaw before, now I have 2 dead in the last year.

 

[Vintage Engine Repairs]

So I was just overjoyed to get my290 to 390 rebuild up and running, I made a few cuts and gave it some rest.
Fired up the 261 to lay down a few trees on the list and it stalled out on me... Weird.

Thinking about it the last time I ran it, it stalled and seemed a little weaker in the cut.
I bought it on Ebay from the seller with the fancy background... Had pics of it with a compression gauge on it. I repeated the same reading when I got it in the mail. Thought that was a good indication of internal conditions... Upon going over it, she looked a little dirtier than any saw I'd ask $400 for.
Since I got it in September I ran a quart of premix 2 stroke fuel and a tank or two of Ethanol free 91 both mixed at 40:1
Pulled the spark plug every time I ran it to check for conditions too...
It stalled mid cut on me today, just like when my 291 died... Pulled the muffler and the rings are scored and so is the piston. A littlehheavy on the carbon in the exhaust port too... I did zero modifications to this one, wanting the pro saw for the resale value when I got my other saw back together. I really don't know what the problem is here...
Can a beat up saw still have good compression for a few runs? Did I get bamboozled by a seller of junk or am I just killing perfectly good equipment?!


What the hell am I doing wrong?!?!
I've never killed a chainsaw before, now I have 2 dead in the last year.

Hi Did you do a pressure and vacuum test when you got it? It’s too late to save it now, but i’d do one before you strip it down. Also you say you are using premix 40-1 and you mix 40-1. Are You certain you are mixing correctly and what premix are you using that is 40-1?

 

[2stroker]

Is the 261 M-tronic?
2stroker

 

[Justin Taylor]

Is the 261 M-tronic?
2stroker

There is m tronic and normal carb

 

[Brent Adams]

Got a 695 Shindaiwa from a coworker. It had 145 psi and started on a prime. Fuel line was melted off. Took the muffler off to clean under it, and the exhaust side was carbon scored to hell. They will sometimes still have decent compression with carbon scoring. Not necessarily that the seller was trying to get you. They may not have pulled the muffler either.

 

[Brent Nowell]

Carbon looks like your culprit judging by the exhaust port and how coked up it is.

 

[Skunkdynamite]

Hi Did you do a pressure and vacuum test when you got it? It’s too late to save it now, but i’d do one before you strip it down. Also you say you are using premix 40-1 and you mix 40-1. Are You certain you are mixing correctly and what premix are you using that is 40-1?

The pre mix came 50:1, I did the math and added a little more mix (Stihl platinum mix)
I bought one of those graduated cylinders that we used to use for our dirt bikes to do the in can mix. Pumped a gallon of E-free at the gas station. Both fuels are in sealed cans since September.
I'll do a vacuum and pressure test before tear it down. At the rate I'm going I really need to do it weekly! Looks like these are easier to do than the homeowner saw is the only good thing.

 

[Skunkdynamite]

Is the 261 M-tronic?
2stroker

Negative...

 

[Skunkdynamite]

Carbon looks like your culprit judging by the exhaust port and how coked up it is.

Is that from running too much oil? Or running rich?

 

[1hander]

man that sux..sorry for your trouble
when i went to my stihl dealer to get 2 stroke mix
i know i need 50to1 they said with the new oil additives and synthetics to use the 40 to 1 mix , in the orange bottle not the silver bottle.
ive been running the 015L i just rebuilt hard and checking for piston problems and found none.

when i get an old saw, i never start it, i always pull the muffler and the cylinder to remove all carbon..that stuff is bad news..
sometimes if the saw has been sitting for a while moisture will rust the inside.
im sure you know but when its running it actually sucks back from the muffler so any debris in there will go back into the cylinder

i went to pick up a used ms270 somethin or other for my dad about 3 months ago.. i was just pulling to feel compression the gent
figured i was having trouble cuz of my one arm situation..and said here let me give you a hand..i said no no
no need to start it please dont start it...... no worries i want you to see your gettin a good saw
grabs the saw...yanks it started, no warm up
and goes to rip on an old test tree he had there , bout 3/4 through it the stops dead
i knew exactly what happened and i explained to him why i didnt want it started

he said its only been sittin for 4 months.. couldnt get it to even turn over after that
but man was i aggravated, i left without a saw

 

[user 122190]

IMO 40:1 is to rich. My ms290 was having problems with 44:1. I mixed up some 50:1 and now it runs perfectly.

Here on this forum, the cult like mentality is 'run it as rich as you can', is without merit.

 

[1hander]

I actually believe you are right.. It runs much better on 50 to 1.. I should gone with my gut and just gone that route.. But I can just use the mixing cup next time I mix some up or ill go to the 50to1 mix in the silver bottle.. To much oil is a bad thing too.. It usually requires leaning the high-speed needle more to get good performance and that where the scarring and seizures come I to play.

 

[user 122190]

I actually believe you are right.. It runs much better on 50 to 1.. I should gone with my gut and just gone that route.. But I can just use the mixing cup next time I mix some up or ill go to the 50to1 mix in the silver bottle.. To much oil is a bad thing too.. It usually requires leaning the high-speed needle more to get good performance and that where the scarring and seizures come I to play.

I don't fully understand why a machine would completely crap out at 40:1, but mine was bogging sometimes at full throttle, rarely, but enough to give me a bad feeling. Switch to 50:1 and never a problem since. The ms461 runs fine with 44:1, but for the sake of simplicity it will now be fed a diet of 50:1

 

[alexcagle]

My gut says the guy before you ran some old stale fuel and possibly too much oil in the mix for a good long while. I'd check that clean spot for a leak from possibly a loose cylinder bolt too.

Which would explain the lean condition heat scoring and glazed ring.
I'm guessing who ever you bought that from knew something was awry, and pled ignorance. That gooey syrup fuel probably made the rings give a normal compression reading until it warmed up and got dry from heat, then it lost compression from glazed over rings.

Not to get into a fuel debate, but unless you buy from a really busy gas station, chances are their non-ethanol fuel is already starting to get stale when you buy it. Or likely doesn't have the mid-grade octane that Stihl recommends.
Really fresh premium fuel from a busy gas station, with the max 5% ethanol in it (by law), is far better for your saw's longevity.

Edit;
Isn't it odd that there are only fines, and no larger wood chips mixed in, where it's stuck to the engine?

 

[rd35]

Hey Skunkdynamite. Something to think about. In the photo I noticed two things. 1) Although a bit scored, your piston rings don't appear to be stuck to the piston.....which will usually give you pretty decent compression even with light scoring. 2) your exhaust port looks wet. Based on those two things I am wondering if you ran this saw really hard (like it is designed to do) and in the process you pulled some gunk out of the jets past the needles which opened them up wider causing an extremely rich mix. This would result in your saw getting flooded out by being overly rich on the H needle and could be the reason for it quitting on you! If it didn't seize then I would check out that possibility. You may need to lean it out a bit and run it. I have ALWAYS run all of my 2-stoke equipment on 50:1 mix and all of my pistons are pristine...even my 260 which has filled my woodshed with 20+ ricks of oak, hickory, and ash annually for the past 20 years! Piston looks almost new...still see all the machining marks! I may be wrong, but I suspect that scoring was possibly there when you bought it and it is just running too rich.

 

[rd35]

Okay now that alexcagle posted this last photo, (had not seen it before posting above) I am not so sure that it was flooded....close up looks like the rings are stuck and exhaust port dry. Thanks for the zoomed in view Alex.

 

[Brent Nowell]

I don't fully understand why a machine would completely crap out at 40:1, but mine was bogging sometimes at full throttle, rarely, but enough to give me a bad feeling. Switch to 50:1 and never a problem since. The ms461 runs fine with 44:1, but for the sake of simplicity it will now be fed a diet of 50:1

There are people here that run at 32:1 with zero problems.
Carbon build up from what I can gather on reading here, and advice given to me, is most likely a tuning problem.
Your probably running too rich a jet setting, and or the engine isn’t getting hot enough to burn off the oil properly.
40:1 is a great mixture that should work well.
It can be said that running rich and running a high oil content mix will give you good lubrication, but it can also lead to high carbon content. Too little oil mixture and too lean of a jet setting will burn an engine up. Tuning is everything

 

[alexcagle]

I wonder if this saw got used commercially, possibly to rip lumber for crating, or dunnage. The short runs could cause the saw to never warm up and create the carbon gunk.

 

[1hander]

yikes that sucker got hot..

 

[foeke]

1:40 instead of 1:50 makes the thing run leaner by just half a %. This thing had a tough life I guess. Maybe it ran hard at a high elevation without a retune.
I'm a *****, so I would just bin it and move on.

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