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Stihl 4-mix trimmer owners, a question

Discussion in 'Lawn Mowing' started by swingset, Aug 24, 2007.

  1. swingset

    swingset LawnSite Member
    Messages: 231

    I'm having a lot of trouble with my 4-mix Stihl's (FS90, FS90R). The first one I bought ran good, so I bought a second, I recently had a thread detailing my troubles with it but suffice to say it was a turd and the dealer took it back and gave me another.

    Well, now both trimmers are running poorly and I'm frustrated.

    Both have good power, idle well, and accellerate well but there's the problem, it's that there's a "gap" in the throttle....namely in between low-idle and rev. If you've got the head turning fairly good, about 10% throttle and you blip it or go to full power, it zips right up to speed. If, however, you've let off the throttle enough that it's down to no spin on the head, and you attempt to gas it up, it bogs, dies, or takes 2 good seconds to get up to speed. Both my FS90's are doing this same thing.

    Has anyone else run into this?

    My dealer has looked both units over, and assures me this is common with these trimmers and it's not a big deal. Well, fair enough if that's true but I've owned 10 trimmers of all makes, including Stihls, and none did this. My old FS45 baby trimmer spins from dead idle to full power in less than a second.

    I'm running good gas, with Stihl Ultra. Both saws are new, but for my own tests I removed the screens to make sure that's not an issue. The carbs are adjusted optimally, or in other words as good as they can be.

    If this is just how the 4-mix Stihls like to run, I can't say I'm too happy....but if it's not systemic with the motors then I'll be leaning on the dealer a little harder to make them right.
  2. LawnBrother

    LawnBrother LawnSite Senior Member
    from SW Ohio
    Messages: 867

    I have not had a problem with mine at all, it runs perfect, but yours sounds like a carb problem. Sorry about your luck but it should be covered under warranty. Don't take no for an answer, that is not normal and needs to be fixed.
  3. MTR999

    MTR999 LawnSite Member
    from Florida
    Messages: 145

    That is why 4-mix is mixed with result and satisfaction around country, my last stihl is FS80 and 85, old-fashioned 2 cycle, from there all are kawasaki and redmax stuff, cheaper and easier to use oil mix, no techno funk and stuff.
  4. rogerwb

    rogerwb LawnSite Member
    from Idaho
    Messages: 94

    I don't have the problem.
  5. aracad

    aracad LawnSite Member
    Messages: 69

    I have the FS90-R and it bogs down on me at times. I can't say I am real happy either. I am hoping it will improve once I break in in a bit more. I guess time will tell.
  6. DaddyRabbit

    DaddyRabbit LawnSite Senior Member
    Messages: 937

    My 110R runs better everytime I use it. Did you remove the spark arrestor screen and are you using premium unleaded along w/Stihl synthetic premix oil?
  7. BeautifulBlooms

    BeautifulBlooms LawnSite Senior Member
    Messages: 613

    I was told ot be sure to use 89 octane fuel or higher.
  8. swingset

    swingset LawnSite Member
    Messages: 231

    Yes and yes. What's weird is both my 90's ran better when new, they've only got about 5 or 6 hours on the pair.
  9. swingset

    swingset LawnSite Member
    Messages: 231

    Makes no difference. I tried 93, 87, 89, didn't notice a shred of difference....other than the 93 octane put a dent in my wallet.
  10. J&T Kiev

    J&T Kiev LawnSite Senior Member
    from N.W In.
    Messages: 416

    My Stihl 4-mix machines run like champs. It could be carburetor related, plugged spark arrestor . Running weak, could be a symptom indicative of the unit needing the value adjustment.

    Has the unit had the valve adjustment procedure ?

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