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Stihl Carb Problem

Discussion in 'Mechanic and Repair' started by Yuanding, Jun 8, 2008.

  1. Yuanding

    Yuanding LawnSite Member
    from England
    Messages: 82

    Among other Stihl stuff, I've got an FS55 trimmer, now 7 years old. It starts and runs very reliably, and never cuts out as some I've seen mentioned on this site with coil problems.
    What has been happening though for about the last two years is that when the day temp gets above about 70F, the idle speed increases to the point where the engine is running at about 1/4 to 1/3 revs.
    I've adjusted the idle screw to its lowest setting and checked the return spring on the throttle, and on the face of it everything is as it should be, but when it's warm it won't idle. The only thing that gets it to return to idle is holding the throttle wide open for a few seconds. But start running the thing at part revs again and the idle speed starts climbing again. I asked my Stihl dealer about this and he said "What are you worried about? It works, don't it? You should be running it at full whack all the time anyway".
    He has a point, but I use the FS55 for mostly light trimming jobs and I don't want to run it at full clout all the time. The main point though is if the cutting head is racing round on idle, it's a bit of a pain as well as a tad dangerous.
    Any suggestions?
  2. johnnie5

    johnnie5 LawnSite Member
    Messages: 29

    its suckin air from somewhere

    start it up and spray wd40 around the carb manifold and over the carb , around the head gasket , when the revs change you have found where its leaking

    idiot dealer should should have known that , its the most common prob with a 2 stroke
  3. Yuanding

    Yuanding LawnSite Member
    from England
    Messages: 82

    Thanks for that. I'll give it a go. Presumably I might be looking at new gasket/sealing ring of some sort?

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