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Author Topic: Stihl Mtronic, vapor lock, die on idle  (Read 424 times)

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Offline Jim Chance

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Stihl Mtronic, vapor lock, die on idle
« on: April 18, 2021, 08:40:52 PM »
I recently bought two new saws, a MS 201CM V3 and an MS 261 CM V2. I have had trouble with both saws using filing station lead free/synthetic.  I am pretty sure a lot of the trouble was vapor lock. The bulb on the 201 would go dry and when I opened the gas tank I could see bubbles coming out of the fuel filter. I switched to premix from the hardware store (expensive!) and they run better, but not perfect. I still have trouble with the both saws dying when bleeping the throttle after cranking and they seem to flood sometimes. So I have a bunch of  questions. First, what are you supposed to do with a vapor locked mtronic saw? I can't put the choke on and pull to get the vapor out because the $%^#ing  computer is controlling the choke and I am not patient enough to just sit there? Second, do these saws flood? It sure acts like it floods when it is warm and running can fuel. Finally, is there some source that actual explains mtronic? Does it control just the mixture and timing or does it control the throttle plate too? Does it have an oxygen sensor and if not how does it "know" when the mixture is right? Does it have temperature and pressure sensors? What does the solenoid do? Does it adjust a needle in an orifice or something else?

Offline Ben Cut-wright

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Re: Stihl Mtronic, vapor lock, die on idle
« Reply #1 on: April 20, 2021, 07:30:12 PM »
I recently bought two new saws, a MS 201CM V3 and an MS 261 CM V2. I have had trouble with both saws using filing station lead free/synthetic.  I am pretty sure a lot of the trouble was vapor lock. The bulb on the 201 would go dry and when I opened the gas tank I could see bubbles coming out of the fuel filter. I switched to premix from the hardware store (expensive!) and they run better, but not perfect. I still have trouble with the both saws dying when bleeping the throttle after cranking and they seem to flood sometimes. So I have a bunch of  questions. First, what are you supposed to do with a vapor locked mtronic saw? I can't put the choke on and pull to get the vapor out because the $%^#ing  computer is controlling the choke and I am not patient enough to just sit there? Second, do these saws flood? It sure acts like it floods when it is warm and running can fuel. Finally, is there some source that actual explains mtronic? Does it control just the mixture and timing or does it control the throttle plate too? Does it have an oxygen sensor and if not how does it "know" when the mixture is right? Does it have temperature and pressure sensors? What does the solenoid do? Does it adjust a needle in an orifice or something else?
Several previous posts and now yours regarding "vapor lock" with little more than conjecture to cause that diagnosis.  You premise the fuel system is in vapor lock, then ask about "flooding".  An intimate knowledge of mtronic won't necessarily be of help if *everything is suspected faulty. "choking the vapor lock out" is a procedure I've never heard.

 
Two "recently purchased NEW saws" should have warranty. Good luck.

Offline doc henderson

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Re: Stihl Mtronic, vapor lock, die on idle
« Reply #2 on: April 20, 2021, 07:50:25 PM »
ben is right, this is a common thread.  take it to the dealer and when they tell you the M tronic is fine, run it and take it back if it acts up.  the dealer should be able to help you trouble shoot.  how old is the saw.  my 261 had to go in several times and tested ok until finally the dealer replaced the solenoid and it has run fine since.  the answer appears to be "no one".  no one seems to understand the M-tronic.  
timberking B 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor 12 volt tarp motor

Offline trapper

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Re: Stihl Mtronic, vapor lock, die on idle
« Reply #3 on: April 20, 2021, 09:13:22 PM »
I took my 261 cm to another dealer and they tested it and said nothing wrong.  Used it today and sometimes dosent start.  let it sit a while and it starts.  No problems with the 241cm.  Orginal dealer kept runing me around until it now is out of waranty.  Second dealer quoted me $75 for mtronic repair kit.  Includes fuel solenoid and fuel filter.  Echo is looking better all the time.
stihl ms241cm ms261cm  echo 310 400 suzuki  log arch made by stepson several logrite tools woodmizer LT30

Offline doc henderson

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Re: Stihl Mtronic, vapor lock, die on idle
« Reply #4 on: April 20, 2021, 09:30:54 PM »
if the problem existed, it should still be under warranty  I guess it depends on how much your time is worth.
timberking B 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor 12 volt tarp motor

Offline Jim Chance

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Re: Stihl Mtronic, vapor lock, die on idle
« Reply #5 on: April 21, 2021, 06:07:29 AM »
Thanks for the comments. I am pretty sure they were vapor locking since (a) they were pushing bubbles out of the fuel filter, (b) had the same problem with two saws on same fuel, (c) bulb was dry on the one with bulb, and (d) changing fuel fixed problem on both saws. Flooding problem came after I switched fuel and no longer had vapor lock. Only used one saw much since then and flooding has cleared up. I am guessing the mtronics got confused and was enriching the mixture for a while? I do like to understand machines I work with and I dont understand mtronics. 

Offline kantuckid

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Re: Stihl Mtronic, vapor lock, die on idle
« Reply #6 on: April 25, 2021, 12:48:05 PM »
I've already posted r. e. my 241 C would start normally cold, then not idle well once warm, then very hard to re-start and balk badly once re-started.
 It's been sitting at my Stihl dealers over a month while they sell mowers for Biden bucks hand over fist. Truckload after load to a mom & pop store. He's (owner) a top tier Stihl mechanic just no time to get back on saws. He does pro logger Stihl saw work more than any other dealer near me. 
Mine came from a pawn shop next to new, ran great until it didn't. It's not a "what gas/mix do I use" issue. 

Anyone have experience with the Echo 501 P chainsaw? 
Kan=Kansas;tuck=Kentucky;kid=what I'm not


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