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Stihl MS270 surging issue - is it the rev limiter?

Discussion in 'Chainsaw' started by 4lane, Jul 12, 2019 at 12:20 PM.

  1. 4lane

    4lane ArboristSite Lurker

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    I have a Stihl MS270 with a rebuilt carb and a new Proline coil (OEM one went bad). It runs well now, and in the cut at WOT it's perfect. But if you're not under load, and squeeze the throttle, it will cut out and on and out and on every .5sec or so. I found it strange that it would be fine at WOT when cutting, so I slowly idled (fine), increased the revs (fine), increased revs even more (fine), then went WOT (not fine) where it immediately would cut in and out.

    Seems like a rev limiter issue. Coil? Any thoughts?
     
  2. dswensen

    dswensen ArboristSite Guru

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    Does the 270 have an air filter with the choke flap built in? I can't recall.

    I had this problem on a Stihl saw and it turned out the return spring on the choke flap was weak. When the engine revved highest, the air volume would pull the choke closed, then the RPMs would drop, and the choke flap would open. Then the revs went up and the cycle started again. Didn't do it when at full throttle in wood because the RPMs didn't get high enough to pull that choke flap shut.

    My solution - still working to this day - was to remove some of the mass from the backside of the choke flap with a dremel, then the spring tension of the flap hinge became adequate to hold it open.
     
  3. SteveSr

    SteveSr Addicted to ArboristSite

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    That is why we generally don't recommend AM coils. You can probably get a good used OEM one off of Ebay for less than an AM. I don't know if that saw had a limited coil on it to begin with. Normally, hitting a rev limiter sounds like 4-stroking which makes it kind of hard to do HS carb adjustments.
     
  4. 4lane

    4lane ArboristSite Lurker

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    No, there is no choke flap on this one. I also pulled the air filter and it ran the same way.
     
  5. 4lane

    4lane ArboristSite Lurker

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    This one has a coil that is impossible to find and expensive from the dealer, but I’m wondering if it’s a coil issue. I’m unsure how the coil and rev limiter are associated.
     
  6. SteveSr

    SteveSr Addicted to ArboristSite

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    The rev limiter is built into the coil. The OEM coil, at least, contains a small microcomputer that handles the timing advance curve. This is why I won't use an AM coil. Why did you change the coil to begin with? They are usually pretty reliable. Sometimes hard to see the spark in a lighted room/shop.
     
  7. 4lane

    4lane ArboristSite Lurker

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    The OEM coil completely failed and had to be replaced. No spark. I’ll look for an oem one over time.
     
  8. SteveSr

    SteveSr Addicted to ArboristSite

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    brad ruch likes this.
  9. 4lane

    4lane ArboristSite Lurker

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  10. SteveSr

    SteveSr Addicted to ArboristSite

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    This is entirely possible. The MS270/280 are Stihl's red-headed step children and are unlike any other saw families. It is a modified clam shell design with the lower case being magnesium rather than the usual plastic housing. As such the saw was used as a test bed for some of Stihl's "New" ideas such as:

    1. Tool-less chain tensioner.
    2. Rear handle chain brake (QS).
    3. Microcomputer controlled ignition timing.
    4. I believe the first M-tronic chainsaw (2006).
    5. Partial spring anti-vibe.
    6. The now infamous Stihl "Flippy-Caps".
    7. Accelerator pump carburetor.

    I don't believe that this saw was ever a big seller hence the shortage of used spare parts. The only thing that you have to watch out for regarding the coil is that the coil & flywheel are different between the regular and M-tronic versions. The M-tronic coil should have at least one (maybe two) extra connections to run the solenoid valve in the carburetor.
     

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  11. DND 9000

    DND 9000 ArboristSite Guru

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    Yes 2006 is right. It was called the intelligent engine management. Only the high speed mixture was regulated through the solenoid valve.
     

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