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MS261C wont start

Crispexx

Crispexx

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Afternoon all,
Might as well start off saying I'm not a Stihl tech and far from one, but I pick things up fairly quickly. I work for a fire department in California and we have A LOT of saws and a few of us are fairly saw savvy despite our lack of professional training. I have access to an SDS and a lot of tools and equipment to basically rival a small, small engine shop, we simply need to knowledge and experience. The InternWeb and YouTube has helped tremendously but i really need confirmation on my thoughts. Now to the challenge! I am trying to fix a MS 261 C-M Z that has less than 8 hours of run time. While it was being ran it began bogging down when the trigger was pulled until it eventually just stopped. Visually everything checks out, nothing obviously broken. When i try to start it on the 'choke' setting it'll pop once per pull for about 3-4 pulls then nothing. after pulling about 5-10 times fuel will start leaking out the exhaust and its plumb flooded. I ran it through the 'check engine sheet' or whatever its called and everything held up like it was supposed to. The station that dropped it off brought by a new black fuel solenoid and i replaced it and the saw fired right up! told then to take the saw and before using it to do a 'reset' of the carb with the 90 seconds idling while on 'choke'. Well...saw was brought back to me and it had been used without being reset and i am back to square one with a saw that wont start and is flooded after 5-10 pulls. I did the test to see if the solenoid was seated properly and it passed, did the leak down test where you pressurize it to .5 bar and count how many pulls to reach 0 and it passed with 7 pulls. I did used the SDS and turned off the solenoid and it held .5 bar will pulling that starter as well. I don't want to just tell the guys they ruined a solenoid and to just get a new one until I'm sure but i wouldn't think a solenoid would go back simply by not resetting that carb. Am I wrong? do they need ANOTHER solenoid and then reset the carb?
 
SteveSr

SteveSr

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Replace the fuel filter with an orange one and try again. I thought that Stihl had an upgrade kit for this. Solenoids don't like fines in them which is why Stihl changed the fuel filter. You may or may not be able to flush the new solenoid by applying a 9V battery momentarily. I am not sure if this carb behaves the same as an non-Mtronic but should hold 7-10 PSI at the fuel inlet indefinitely. If not it will let gas into the saw and cause flooding.
 
Crispexx

Crispexx

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Replace the fuel filter with an orange one and try again. I thought that Stihl had an upgrade kit for this. Solenoids don't like fines in them which is why Stihl changed the fuel filter. You may or may not be able to flush the new solenoid by applying a 9V battery momentarily. I am not sure if this carb behaves the same as an non-Mtronic but should hold 7-10 PSI at the fuel inlet indefinitely. If not it will let gas into the saw and cause flooding.
I replaced the fuel filter with the orange one today. I did a bleed down test where you pressurize it to about 7 psi and it should hold with no bleed down for 20 seconds and i did that and it was good.
 
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Spoon Carving With Tom

Spoon Carving With Tom

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It should hold steady at 7psi under vacuum and pressure. Check for air leaks at the seals and replace if necessary. If it’s tuned out and you keep running the saw, it will cause excessive wear at the bearing as the unmetered air passes and prohibits full lubrication.
 
farmer steve

farmer steve

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Afternoon all,
Might as well start off saying I'm not a Stihl tech and far from one, but I pick things up fairly quickly. I work for a fire department in California and we have A LOT of saws and a few of us are fairly saw savvy despite our lack of professional training. I have access to an SDS and a lot of tools and equipment to basically rival a small, small engine shop, we simply need to knowledge and experience. The InternWeb and YouTube has helped tremendously but i really need confirmation on my thoughts. Now to the challenge! I am trying to fix a MS 261 C-M Z that has less than 8 hours of run time. While it was being ran it began bogging down when the trigger was pulled until it eventually just stopped. Visually everything checks out, nothing obviously broken. When i try to start it on the 'choke' setting it'll pop once per pull for about 3-4 pulls then nothing. after pulling about 5-10 times fuel will start leaking out the exhaust and its plumb flooded. I ran it through the 'check engine sheet' or whatever its called and everything held up like it was supposed to. The station that dropped it off brought by a new black fuel solenoid and i replaced it and the saw fired right up! told then to take the saw and before using it to do a 'reset' of the carb with the 90 seconds idling while on 'choke'. Well...saw was brought back to me and it had been used without being reset and i am back to square one with a saw that wont start and is flooded after 5-10 pulls. I did the test to see if the solenoid was seated properly and it passed, did the leak down test where you pressurize it to .5 bar and count how many pulls to reach 0 and it passed with 7 pulls. I did used the SDS and turned off the solenoid and it held .5 bar will pulling that starter as well. I don't want to just tell the guys they ruined a solenoid and to just get a new one until I'm sure but i wouldn't think a solenoid would go back simply by not resetting that carb. Am I wrong? do they need ANOTHER solenoid and then reset the carb?
Not sure if I'm reading this correctly. After the first pop on choke it should be moved to the run position.
 
Crispexx

Crispexx

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It should hold steady at 7psi under vacuum and pressure. Check for air leaks at the seals and replace if necessary. If it’s tuned out and you keep running the saw, it will cause excessive wear at the bearing as the unmetered air passes and prohibits full lubrication.
Yea I'm going to try the vac and pressure test again today to make sure I didn't mess up
 
Crispexx

Crispexx

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Find another 261 if possible and swap the coil then the carb and see if that fixes it.
That's what I would like to do is try swapping out the carb. We also have a bunch of 462C's and 362's so i have a ton of parts for those, but this is the first 261 I've had dropped off so parts around here are almost non existent for now.
 
lone wolf

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That's what I would like to do is try swapping out the carb. We also have a bunch of 462C's and 362's so i have a ton of parts for those, but this is the first 261 I've had dropped off so parts around here are almost non existent for now.
This is why I have a couple of each saw so I can swap parts. But it does sound like ignition to me but only a guess at this point.
 
Crispexx

Crispexx

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well a new development today, after sitting over night and most the working day one of the other guys took the bar and chain off and took it outside to try and start it, and it started! he was able to rev it a little bit so he shut it off and put it on the cold start to run a reset. the idea was to reset it so if the setting were messed up it would bring it closer to factory so we had a better chance of getting it started more regularly. Anyways, when he shut it off he pushed from Choke straight to off. correct me if I'm wrong but with those you let them run their 90 seconds then tap the trigger to get it of choke then turn it off correct? my worry is if he forced the carb from choke to off without popping the trigger it was all for not. either way after all that it would not run off of choke. then after a few starts it stopped starting again and continued to flood again. So tomorrow after letting it sit over night again i'll give it another twirl and see if i can get it to reset.
 
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