Stihl MS 261M Tronic idling very fast

[big dawg Jesse]

Hey, guys hope everyone is doing well. I have a Stihl MS 261M Tronic chainsaw that I am working on. The complaint from the customer was idling fast coming off of throttle starts up fine and runs good just idles fast. It almost sounded like there was an air leak causing it to run lean. So I did a pressure vacuum test and blocked off the decompression valve. It held pressure and vacuum overnight perfect no air leaks. Started it with the decompression valve blocked off and it did the same thing. After about a minute or so it eventually Idled down but as soon as I give it throttle and let off the same thing happened. Did Mtronic reset twice made no difference. Took the muffler off the piston and the cylinder looked to be in great shape changed the spark plug air filter checked the fuel filter was clean put pressure to the carb to make sure the needle was sealing and it was. I am scratching my head. Any ideas are appreciated
Thanks

 

[ammoaddict]

I know nothing about mtronic saws. Is the idle control a solenoid or some type of linkage that could be hanging up?

 

[big dawg Jesse]

I know nothing about mtronic saws. Is the idle control a solenoid or some type of linkage that could be hanging

I know nothing about mtronic saws. Is the idle control a solenoid or some type of linkage that could be hanging up?

checked every linkage possible because that is the first thing I thought of

 

[Tobystihl]

Replace fuel solenoid and replace fuel filter with the upgraded orange one

 

[ammoaddict]

Replace fuel solenoid and replace fuel filter with the upgraded orange one

Interesting, so mtronic saws use special fuel filters?

 

[big dawg Jesse]

Replace fuel solenoid and replace fuel filter with the upgraded orange one

Thanks I will look into that

 

[big dawg Jesse]

Replace fuel solenoid and replace fuel filter with the upgraded orange one

Thank you I will look into that

 

[Tobystihl]

Interesting, so mtronic saws use special fuel filters?

Stihl uprated to much finer filtration after the earlier solenoids were getting gummed up and sticking due to fine debris remaining in the fuel after filtration !

 

[Tobystihl]

Thank you I will look into that

What is most likely to be happening with your saw is the solenoid is sticking, resulting in it not allowing the saw to return to idle!
Hope you get it sorted

 

[ammoaddict]

Stihl uprated to much finer filtration after the earlier solenoids were getting gummed up and sticking due to fine debris remaining in the fuel after filtration !

I see, thanks for explaining.

 

[user 122190]

So is this an ethanol problem? M-tronics is more sensitive to ethanol?

 

[user 122190]

Might be a good idea to start using this if your pump gas is not up to high standards.

 

[Vintage Engine Repairs]

So I did a pressure vacuum test and blocked off the decompression valve. It held pressure and vacuum overnight perfect no air leaks.

Guinness Book Of Records for the longest recorded pressure and vacuum test ever conducted, though I’m not sure how it held pressure and vacuum at the same time?

Joking aside, did you rotate the crank a number of times during the vacuum test? Have you changed fuel filter and pressure tested the fuel line, impulse line and carb? Are you using good quality fresh fuel? Have you had a look in the carb for junk? Leaking main nozzle check valve? Stiff diaphragms? Is the needle lifting and sealing as it should? Is the lever set at the right height? Is the fuel line or impulse line even slightly bent / kinked? Are both oem? Is the fuel tank vent partially blocked? Is the fuel or impulse lines very soft or very hard? Have you tested to ensure you’re getting a good impulse? Is the pump diaphragm good? If all the above checks out, try a new solenoid.

 

[big dawg Jesse]

Guinness Book Of Records for the longest recorded pressure and vacuum test ever conducted, though I’m not sure how it held pressure and vacuum at the same time?

Joking aside, did you rotate the crank a number of times during the vacuum test? Have you changed fuel filter and pressure tested the fuel line, impulse line and carb? Are you using good quality fresh fuel? Have you had a look in the carb for junk? Leaking main nozzle check valve? Stiff diaphragms? Is the needle lifting and sealing as it should? Is the lever set at the right height? Is the fuel line or impulse line even slightly bent / kinked? Are both oem? Is the fuel tank vent partially blocked? Is the fuel or impulse lines very soft or very hard? Have you tested to ensure you’re getting a good impulse? Is the pump diaphragm good? If all the above checks out, try a new solenoid.

It wasn't at the same time two different tests LOL yes I did pull the rope during the pressure and vacuum Test no drop. The fuel line is good and everything else checked out when I had the pressure vacuum tester out I wanted to make sure I covered all my bases. I just got a price on a new solenoid today the white one with the upgraded fuel filter is $19 Canadian.

 

[DND 9000]

Stihl uprated to much finer filtration after the earlier solenoids were getting gummed up and sticking due to fine debris remaining in the fuel after filtration !

Yes the filtration is finer now, but the valves don`t stick. That`s wrong information. The valves leak (the black ones), because of wear through fine dirt in the sealing area (made of polymer). Sticking may be possible if it is not operated for a long time and a mix with an oil that can harden is used. But this is really really rare and not an existend problem. Idling problems or lacking power under full throttle is because of the leaking and an overly rich condition.

 

[TRTermite]

Yes the filtration is finer now, but the valves don`t stick. That`s wrong information. The valves leak (the black ones), because of wear through fine dirt in the sealing area (made of polymer). Sticking may be possible if it is not operated for a long time and a mix with an oil that can harden is used. But this is really really rare and not an existend problem. Idling problems or lacking power under full throttle is because of the leaking and an overly rich condition.

Reading from start to here Post #4 And Post #8 Mostly agrees with post#15 except for the technical definition difference of "Sticking" verse "Leaking" To me this thread as a whole has been informative to me as someone that knows VERY little about m tronics. Thanks everybody

 

[big dawg Jesse]

Yes the filtration is finer now, but the valves don`t stick. That`s wrong information. The valves leak (the black ones), because of wear through fine dirt in the sealing area (made of polymer). Sticking may be possible if it is not operated for a long time and a mix with an oil that can harden is used. But this is really really rare and not an existend problem. Idling problems or lacking power under full throttle is because of the leaking and an overly rich condition.

Thank you very much for the useful information I'm going to try that and see what happens I have ordered the white one and the upgraded fuel filter I have to go get it on Thursday so I will let you know thanks

 

[big dawg Jesse]

Hey, guys got the new upgraded white fuel solenoid and filter in today and the saw idles down right away just as it should thanks for all your help!

 

[ammoaddict]

Awesome. Thanks for the update.

Sent from my moto g(7) power using Tapatalk