Stihl MS261c M-Tronic Won’t Idle

[NHden]

Sorry - old thread but relevant as a reference.

FYI - most Mtronics parts are free ! (read up on the labor, it's also covered with caveats)

The owner's manuals for the Mtronic saws have a section on the emissions warranty, parts and labor. Thanks (or no thanks) to EPA, all emission related items are covered for 2 years ! I'm including the list here for the MS201TC-M and perhaps someone can make it sticky in a new thread? Stihl's manuals are all over the place. Not all revisions include this:

STIHL Incorporated Federal Emission Control Warranty Statement

The following list specifically defines the
emission-related warranted parts:
– Air Filter
– Carburetor (if applicable)
– Fuel Pump
– Choke (Cold Start Enrichment
System) (if applicable)
– Control Linkages
– Intake Manifold
– Magneto or Electronic Ignition
System (Ignition Module or
Electronic Control Unit)
– Fly Wheel
– Spark Plug
– Injection Valve (if applicable)
– Injection Pump (if applicable)
– Throttle Housing (if applicable)
– Cylinder
– Muffler
– Catalytic Converter (if applicable)
– Fuel Tank
– Fuel Cap
– Fuel Line
– Fuel Line Fittings
– Clamps
– Fasteners

 

[Abbeville TSI]

I have seen that list, most o*p*e* has a similar one. I don't have any confidence in my local dealers to take care of problems in a timely manner.
The Echo dealer seems to be labor poor with a concentration on mowers, and the two Stihl dealers are parts of a chain of stores. One is an Ace Hardware and the other sells green and yellow tractors. I have no gripes with the stock on the shelves at either place, the tractor guys take care of me for parts.
I haven't needed any of them for service, and wonder if Father Stihl requires them to have complete diagnostic and service tools at all stores or just the "home dealership". Maybe @Stihl Gold Tech knows the answer...

 

[stihltech]

WELL- they are SUPPOSED to have a certified tech on staff BUT that is not the case around here. If they are a chain, there may be one in another store miles away. Statement to a customer from a local store. "We send it to XY repair shop and if he can't fix it, we send it to ABC shop."
Nothing against any JD store but are you going to repair 100,000 dollar tractors or 400 dollar chainsaws first?
Meanwhile, I am having a hard time finding space in the shop for all the repairs. Turning away off brands at this time.

 

[Abbeville TSI]

I fully understand keeping the farmers going is the primary job of a tractor dealership, and I know not to bother the parts counter at planting or harvest time. And that is the exact reason I do my own repairs after working at a real saw shop part time for years. My job mainly was to support the loggers that bought their saws there. I worked nights rebuilding saws, repairing bars, making chain loops and occasionally sharpening chains. The boss did the bucksaw chains, he knew it was boring and wanted me on the service end. Many a night at 10:00 a logger would come by with a pile of saws or starter covers and plead for me to get some of done...When I started he was selling Pioneers, P52's and such, then Huskies and finally Stihl. He also sold and serviced Toro mowers, and Echo trimmer and blowers. I didn't do much of that, because loggers... Then the loggers went mechanized (don't blame them) and my days of local renown ended...
Back to the tractor fixers for a minute- when the techs are busy with ag stuff, who gets to work on the saws and trimmers? Right, I looked in the back of enough shops to not want my stuff fixed by Bubba. Now I was never fortunate enough to go to a factory school, but coming from ten years of automotive heavy repair I knew the basics and the boss showed me ins and outs of two stroke repair. All that ended in the late 80's/ early 90's. I am still remembered though- Oh yeah you used to work on my daddies saws and such.

 

[singinwoodwackr]

Well, I think I’ve got it figured out. A year ago I built 3 other 261s from throw away carcasses. After ordering ebay carb kits and rebuilding carbs I couldn’t get any to run. Turned out the kits were wrong…and still sold, by the way. Correct kit, fired right up.
I tried 2 different regular carbs after swapping all the MT stuff out…no joy. My guess is that I used what was in my misc kit pile when I checked carbs I had and none of what I had was correct. Looked close, but…
have reordered the right kits so will see what happens.

Follow up…
non-mtronic
no joy with the new carb kits. All the kit parts are duplicates of the OE parts, unlike in the earlier thread I posted.
I even tried another OE donor carb, used…same problem
the carb is getting gas. It will idle, sort of, but when trigger is pulled it dies. Id figure a fuel delivery issue so redid a tank pressure and vac test…all good. Collapsing fuel line? Top line seemed ok so reused it. Inner line was replaced with oe. Stumped

mtronic
tried another used carb. It started and went into reset mode…for about 5 sec and then died. Won’t restart.
im going to try a new green solenoid next.

I think these saws are simply cursed. May just put them up on eBay and be done.

 

[SteveSr]

Follow up…
non-mtronic
no joy with the new carb kits. All the kit parts are duplicates of the OE parts, unlike in the earlier thread I posted.
I even tried another OE donor carb, used…same problem

Was the used donor carb confirmed to be good on another saw?

the carb is getting gas. It will idle, sort of, but when trigger is pulled it dies. Id figure a fuel delivery issue so redid a tank pressure and vac test…all good. Collapsing fuel line? Top line seemed ok so reused it. Inner line was replaced with oe. Stumped

This sounds like a main nozzle check valve that is stuck closed. It will idle all day but never rev up. This is a non-fixable carb fault.

mtronic
tried another used carb. It started and went into reset mode…for about 5 sec and then died. Won’t restart.
im going to try a new green solenoid next.

I think these saws are simply cursed. May just put them up on eBay and be done.

Have you thoroughly checked the wiring harness? If the saw fails the harness continuity test it will kill the spark.

 

[singinwoodwackr]

Wiring all checked
4 different
carbs all do this
All rebuilt, some 2x
May have screwed up the rebuild
So, the check valves on these carbs are not serviceable? That sucks.
I use a sonic tank with carb cleaner to clean used carbs. I wonder if in blowing them out afterwards I killed the check valves.

update:
new green solenoid and it runs, wee!

now to figure out the other saw…

 

[singinwoodwackr]

Well figured I had the parts, so…swapped the non-mtronic to an mtronic using the used carb that finally showed up. Fired right up and reset as normal.
so, I have definitely screwed up the regular carbs somehow, sigh…
now have 2 running mtronic saws and a pile of dead carbs

parts swapped:
coil, carb and harness
air deflector

 

[SteveSr]

so, I have definitely screwed up the regular carbs somehow, sigh…

Hitting them with high pressure shop air can definitely damage carbs. The most that I ever use is a spray can of carb cleaner.

Sonic tank could possibly cause issues as well if there are any small parts that could rub against each other and wear. Of course, this would be specific to the model of carb; i.e. I would never put a M-tronic solenoid in a sonic tank.

 

[singinwoodwackr]

It is odd. I've rebuilt other 261 non mt carbs using the same procedure...all good.
But, I do think they were a different model...ones with 2 caps rather than just the one on the hi screw that all of these have.
O well.

 

[NHden]

Sorry, kinda late to the party. I'm not familiar with the internal structure of the solenoid (yet) but will be soon. I'm wondering if compressed air may have reached and distorted whatever sort of "flapper" is driven by electromagnet. When the solenoid drive requests fuel, it gets a deluge and dies.

Many of our mothers told us not to put Q-tips deep into our ears (or maybe it was a pencil). Likewise, never put compressed air into carb openings except for a gentle puff from a distance, and at an angle.

 

[singinwoodwackr]

Sorry, kinda late to the party. I'm not familiar with the internal structure of the solenoid (yet) but will be soon. I'm wondering if compressed air may have reached and distorted whatever sort of "flapper" is driven by electromagnet. When the solenoid drive requests fuel, it gets a deluge and dies.

Many of our mothers told us not to put Q-tips deep into our ears (or maybe it was a pencil). Likewise, never put compressed air into carb openings except for a gentle puff from a distance, and at an angle.

there is an exploded view of all three of the Stihl solenoids in one of the bulletins posted in the 'Stihl information' thread...I'll try and find it and add...

 

[ZeroJunk]

Haven't looked at a MS261, But according to PartSmart there are 10 different part numbers for carbs for a MS251

 

[NHden]

Thanks. Appreciate it.

 

[stihltech]

Looking up parts for Stihl almost requires a serial number to be used. It will select the the correct part (as in the many carburetors for some models).