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Stihl FS 90r running weird

Discussion in 'Mechanic and Repair' started by pclawncare, May 8, 2007.

  1. pclawncare

    pclawncare LawnSite Senior Member
    Messages: 991

    My stihl fs90r 4 mix has been running a little weird for the last week or so i know its not the carb or anything it runs great at WOT but when i walk from one area to the other it sometimes dies. Also it has been a little harder than normal to start and a couple times i have pulled on it and it has compression and then i cant get it to go any more i have to let the string recoil and give it a good jerk. This trimmer is just now one full season old i would guess 300-400 hours of operation. Does anyone think that the valves need to be adjusted? Any other ideas what could be going on here?
  2. khouse

    khouse LawnSite Bronze Member
    Messages: 1,465

    If it has a spark arrester screen - it may be plugged? If so clean or remove it.
  3. pclawncare

    pclawncare LawnSite Senior Member
    Messages: 991

    No screen i have already taken care of the problem.
  4. Andyshine77

    Andyshine77 LawnSite Member
    Messages: 147

    Hi pclawncare

    You need to use a compression tester. If the top end is bad it can produce tons of friction, yet have no compression.
  5. pclawncare

    pclawncare LawnSite Senior Member
    Messages: 991

    Andy thanks and how do you like your br600 i have been looking at them just havent forked over the 500 for it yet
  6. Andyshine77

    Andyshine77 LawnSite Member
    Messages: 147

    I love it. I did have some problems with the valves at first but my dealer took care of the problem, and sense then I've had no other issues. I've had the blower for about a year now.
  7. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    What about the air filter and the spark plug, those two things can make it run funny if they're about in need of replacing. If in doubt, replace anyway, won't hurt to be sure.
  8. Jay74

    Jay74 LawnSite Member
    Messages: 57

    Decarbon cylinder and valves. Adjust valves. Also have a mechanic go through the carb and verify that your check valves are operational. After all that run stihl ultra oil - good stuff!

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