Need help with Stihl 261

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rms2

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Greetings! I've been lurking here a long time and have learned a huge amount from all the knowledgeable folks here but this may be my first actual post, and first time I've really been stuck on something in a while. A friend who works in resource mgmt for a local farm asked if I could help with his Stihl 261, non-running, so he took it to the local dealer where it has sat without getting any attention for 2 months. So I offered to have a look. (And this saw is not beat, he says probably under 30 hours total time on it) I checked all the basics; clean air filter, clean muffler, new fuel filter, fresh fuel, good spark. And here is where it gets more complicated. He said he was in a hurry last time it ran and may have used fuel with no oil mix by mistake, he's not sure, may have been mix fuel or not. Though he always runs non-ethanol from the local farm store. Looking at the piston through the exhaust port it looks not bad, maybe slightly scuffed but still mostly shiny. Compression is 65 and holds. Seems like it should at least run a little bit with all that covered. So on cranking I get nothing. And then with full choke multiple pulls it is not flooding - spark plug is not wet. Seems to not be getting fuel to the cylinder. Carb settings are within normal range. So I try to pull the carb and have a look. But the carb is held on by 2 pesky little 8mm nuts down inside a plastic manifold between the air filter and carb. There must be a special Stihl tool to remove them because none of my 8mm sockets fit without a real struggle, they are just a little too large in diameter, it would take a really thin walled 8mm socket to get into there. But I finally got the carb off, it's not badly varnished at all. I cleaned it out best I could with carb cleaner, reinstalled and still no fire, and no fuel to the cylinder best I can tell after cranking with full choke multiple times to be sure. So now I need; 1) The special Stihl 8mm carb tool for those pesky nuts, 2) A new black plastic manifold for between the air filter and carb because my 8mm socket is hopelessly stuck in there now. 3) A new diaphragm for the carb, maybe? 4) Advice on what it is I am over looking, and recommendations on where to get these parts, and possibly a new top end kit if the piston looks horrible when I pull the cylinder. And I've searched through the service manuals postings here but haven't found the 261 yet, apologies if it is here and my search skills are lacking. Thanks!
 
Yea make sure you have an appropriate pressure gauge, I did that with a cheap gauge from Amazon and it gave me a super low reading, turns out it wasn’t designed for those little engines. Another “redneck” test is pick it up by the starter and if it has decent compression it should either not fall or fall slowly


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Wow! That was quick, thanks fellas! Not sure about my gauge, not a cheap one, it's been accurate on the dirt bikes and bigger saws but I need to compare it to another one or two compression gauges to be sure. Really appreciate the links to the manuals. And I'll go put a little mix in the carb and see what happens, good idea. And it passed the redneck compression test, doesn't fall, thanks!
 
Found this post with info on the carb nuts, good info in case somebody else runs into this issue;

https://www.arboristsite.com/thread...-nuts-of-air-filter-baffle-on-a-ms261.275738/
And of course Stihl does make a T handle driver for this purpose, found one on fleabay for $15, not available from your local dealer - at least not mine.
A 5/16”, 1/4” drive socket works.
but, I just ground down my 8mm until it fit :p
as for compression…bet your adapter isn’t sealing properly. Make sure everything is tightly sealed on the tester.

carb not getting fuel? You may have the same bad gasket kit I did…check my thread from a few weeks ago. Previous owner had ordered an eBay kit and is was wrong…didn’t know it. I had ordered the same kits…seller is still doing this, by the way. eBay’s fraud dept is a joke.

https://www.arboristsite.com/threads/carb-not-getting-fuel.359538/page-5
 
A 5/16”, 1/4” drive socket works.
but, I just ground down my 8mm until it fit :p
as for compression…bet your adapter isn’t sealing properly. Make sure everything is tightly sealed on the tester.

carb not getting fuel? You may have the same bad gasket kit I did…check my thread from a few weeks ago. Previous owner had ordered an eBay kit and is was wrong…didn’t know it. I had ordered the same kits…seller is still doing this, by the way. eBay’s fraud dept is a joke.

https://www.arboristsite.com/threads/carb-not-getting-fuel.359538/page-5
Surprise, Chinese parts :rolleyes:.
 
Hi the 261 has a decompression valve try starting with it closed it’s only a small saw should be much of a problem,
my 261 has 205 psi
I’d check the rings are moving in and at through the exhaust port they should move in below the diameter of the piston,
Next get your biggest pistol drill put a 13mm socket on it pull the recoil of put the socket on the flywheel nut & saw in the off position & with the decomp open run the saw with the drill in reverse
at say 750 rpm
See if it will pull fuel into the cylinder
 

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