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MS250 oddity

Discussion in 'Chainsaw' started by Patrick62, Mar 14, 2019.

  1. Patrick62

    Patrick62 Addicted to ArboristSite

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    Gentlemen,
    I would like to share a recent experience I had at the store. A 250 was brought to me "needing a tune up" he said. I was willing to wager that the carb had junk in it (there was a little, but not terrible). I went ahead and did the "small engine check" for the fun of it, and to show a newbie how things work.

    We discovered that the flywheel was set a fair distance from the flywheel. Enough that I went ahead and reset it to specs with the provided Stihl gauge. Cleaned and replaced the diaphram in the carb, and was ready to go.

    Went out and gave it a pull. Clunk. :wtf:

    Went back in, whipped out the torx driver and pulled the starter and found this: IMG_0171.jpg
    It's a little flat nub that sticks up from the opposite side of the flywheel about .020+
    And now I understand why it had the magneto set out so far... Well.... what to do? I decided that I would just file that sucker off! IMG_0173.jpg

    Put it back together witht he magneto gapped coccectly, and the saw runs like a watch now. He picked it up last Sunday and told me that it had locked up on him once as well. Oh really.... how interesting. Told him what I had found, and how I fixed it.

    Curiosity got the better of me at this point and I checked the two MS250's we have on the shelf, and guess what I found?? IMG_0175.jpg

    I call it "casting flash" for lack of a better term, but I don't think it is supposed to be there. Further, I don't thing that the magneto should be spaced far enough to clear this thing! Two wrongs do not make it right!
     
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  2. alexcagle

    alexcagle Cutoff Saw Specialist

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    Made in USA plant too.....:(
     
  3. rd35

    rd35 Just an average Joe's brother!!

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    I wonder if the Farmertec flywheels have that exact same flaw!?? :nofunny: Also wonder if grinding off that flaw affects balance!??? :eek: Sorry just thinking out loud through the keyboard.:D
     
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  4. Sam R

    Sam R 8mm Socket

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    How did it run with that hitting the coil? Or did it originally clear the coil. Seems like the two striking would be enough to shear the key.
     
  5. ironman_gq

    ironman_gq Addicted to ArboristSite

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    I'm wondering if that isn't there by design, use it to set the gap on initial assembly? Strange thing to see though.
     
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  6. Wood Doctor

    Wood Doctor Edwin

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    That's what it would appear to be. The idea is to use that rise to set the gap on the coil with the flywheel not bolted on yet. Then when the flywheel is next dropped in place, this rise will clear the coil. Frankly, I've never seen this on other Stihl flywheels. Check to see if it sticks up about 0.01".

    I also checked my MS251C flywheel and it has no such rise on it. Could be that Stihl gave up on the idea.
     
  7. Patrick62

    Patrick62 Addicted to ArboristSite

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    I checked a few other saws at the store this morning. All is good, it seems to be specific to the 250's
    My specs call for .008 on the gap at the magneto to flywheel on magnet side. IF the gap is set correctly the engine will not turn.
    So, it appears that the factory compensated with the LARGE gap to clear the protrusion... Which might produce a weak spark.
     
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  8. Wood Doctor

    Wood Doctor Edwin

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    Sorry, I made a typo (poor one at that). 0.01" is very close (not 0.02" that I corrected). Some even say 0.009", but I never have any problems with 0.01" on about any saw that I work on.
     
  9. Leerod83

    Leerod83 ArboristSite Operative

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    I've heard that 250s are easy to flood cold starting. If the bigger gap is causing a week spark you recon that might be why they flood easily? Just thinking aloud here.
     
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  10. Wood Doctor

    Wood Doctor Edwin

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    I believe it is the 251 that floods easily (including mine). I like your idea, however. A weak spark can lead to easy flooding. Occasionally that spark could even skip so that no fuel mixture is ignited that time around.
     
  11. Patrick62

    Patrick62 Addicted to ArboristSite

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    The little 250 is usually a consistent performer from what I have seen around here. However, a weak spark will make things a little more dicey.
    .010 would be just peachy, but I am not exagerating and will check the next time I look at one of these... I am guessing they are out around .025 to .035 to clear the casting flaw.
     

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