Sthil FS90

Discussion in 'Lawn Mowing' started by blake101, Jun 4, 2011.

  1. blake101

    blake101 LawnSite Senior Member
    Messages: 581

    Okay Hard to start and will sometimes die at idle, do I need to adjust the valves, or look at the carb?
  2. Ridin' Green

    Ridin' Green LawnSite Fanatic
    Male, from Michigan
    Messages: 17,829

    Try adjusting the idle screw up a little bit. It probably has vibrated of its original setting to too low a speed.
    Just follow the owners manual instructions, or go online to Stihl and check them there.
    Last edited: Jun 5, 2011
  3. Grasman

    Grasman LawnSite Member
    Messages: 47

    When the same thing happens to my 110's and 90's I adjust the valves and change the air filters.
  4. MowHouston

    MowHouston LawnSite Bronze Member
    Messages: 1,012

    I agree with the air filter too. A lot of the time if I change the air filter it does wonders. Especially in this drought down here.
  5. mictrik

    mictrik LawnSite Member
    Messages: 245

    Check air filter. Have you been using a good synthetic oil like Stihl "Ultra"? If not, check the muffler & screen. You may want to look at the exhaust valve to see if it's excessively carbon-ed. Check spark gap, check valve clearance ( but this does not have to be done often). when it is running & you depress the throttle does it hesitate or respond quick? if it hesitates you may want to check the low speed needle & lean slightly. If it is excessively humid & the carb was adjusted in winter dry conditions this could be the case, though i doubt it.
  6. blake101

    blake101 LawnSite Senior Member
    Messages: 581

    Thanks for the information. It does hesitate a little, I will try the low speed needle.
  7. blake101

    blake101 LawnSite Senior Member
    Messages: 581

    Okay Cranks great. When it is cold the throttle responds quick, but as soon as it warms up it will hesitate. Does any body have any solutions. I did adjust my valves and changed air filter and new spark plug. It just takes to long to rev-up.
  8. alexschultz1

    alexschultz1 LawnSite Bronze Member
    Messages: 1,588

    check the muffler and make sure its not clogged at the end, take the screen out and check it.. may be an issue with a magnito clearance. maybe.. its pretty rare for that to happen on 2 strokes.
  9. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,592

    Did you adjust the low speed needle? I assume you have one? If it starts good and accelerates after starting then you got enough gas. If it bogs after it warms up then shut down the low needle a little bit. I doubt that you have both a low and high needle......that is the advantage of units with those so you can tune for weather conditions.
  10. finneylawns

    finneylawns LawnSite Member
    Messages: 59

    Check out this post.

    I posted this about my issues starting my weedeater and edger.

    I currently have them at my local Stihl dealer for service, being that they are under warranty. I will post their finding hopefully on Monday.

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