Stihl FS90R 4mix new owner ?

Discussion in 'Lawn Mowing' started by jstew33, Apr 24, 2012.

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  1. jstew33

    jstew33 LawnSite Member
    Posts: 24

    I took the plunge and bought my first Stihl trimmer. Very different beast from the Redmax trimmers I've been using. I have run 5 tanks of quality fuel with Stilhl HP oil and I have a concern regarding the smoothness of engine. 3/4 throttle and the unit runs nice and smooth, but full throttle and the engine housing starts shaking violently and sounds like it's missing. Full throttle in heavy growth it runs fine, but when it's only light trimming duty it starts acting up. I also switched to some .105 line and that seemed like it added enough load to smooth it out some at full throttle. I took it back to the dealer to have them look at it and 2 minutes later they brought it back and said all is fine. I've also noticed that it will stumble for a split second when testing from various throttle positions to WOT. This is the first 4mix tool I've laid my hands on, so really not sure if it's truly and issue or not.
     
  2. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    It's fine. It's hitting the rev limiter at full throttle.
     
  3. MTenterprises

    MTenterprises LawnSite Senior Member
    Posts: 326

    I have the same trimmer and it does best at full throttle. They are not built to idle or feather much. They load up. Just my experience. :usflag:
     
  4. ScaggyGrass

    ScaggyGrass LawnSite Member
    Posts: 54

    I have a FS90.. and the dealer says it needs a valve ajustment after first 20 hours..
     
  5. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    Hmm.. The manual says 130 hours. If he's willing to do the valve adjustment for free then by all means, let him do it. The valve adjustment is simple and easy though. Even a cave man can do it.
     
  6. GMLC

    GMLC LawnSite Platinum Member
    Posts: 4,353

    Richard is 100% correct. Your hitting the rev limiter at full throttle with no load. Mine does the same thing.
     
  7. Ridin' Green

    Ridin' Green LawnSite Fanatic
    Male, from Michigan
    Posts: 13,275

    So does mine, but mine only does it with the edger attachment mounted. It is nice and smooth at WOT with the trimmer head. I guess the trimmer head places a bit more load on it than the edger.

    The one and only recommended valve adjustment is needed at 139 hours according to the ops manual, or as needed at any other time outside of that.
     
  8. GMLC

    GMLC LawnSite Platinum Member
    Posts: 4,353

    Strange, mine does it with the trimmer head. Ridin' do you have your guard off?
     
  9. Ridin' Green

    Ridin' Green LawnSite Fanatic
    Male, from Michigan
    Posts: 13,275

    No, I'm one of those guys who leaves all that stuff in place.:)
     
  10. GMLC

    GMLC LawnSite Platinum Member
    Posts: 4,353

    Me too. What size string?
     

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