Stihl primer bulb going dry

Discussion in 'Mechanic and Repair' started by unkownfl, Aug 18, 2010.

  1. unkownfl

    unkownfl LawnSite Gold Member
    Messages: 3,837

    I have a fc90 and a fs90r, the fc the bulb goes dry and only has air even when I pump it. It doesn't fill-up with fuel like the fs90r. I think this is contributing to hard starting. The fs starts first or second pull while the FC may take up to 15 or so pulls hot or cold. I have done all preventative maintenance and still can't get the fc to start properly. I believe this issue is causing the hard starting, so what is causing it to do this?
  2. mowerknower

    mowerknower LawnSite Senior Member
    Messages: 766

    sticking check valve internally in carb, Replace carb
  3. Ruben Rocha

    Ruben Rocha LawnSite Senior Member
    Messages: 577

    Or a leak in the fuel line in the gas tank.
    If you pump the bulb and it sticks a bit then it would be a carb issue.
    Sometimes I have found to rotate the hi and low screws a few times and it works okay again.
    If you attempt to take the spacer block off and clean it, be careful if you blow it out with compressed air. To much pressure may blow out the check valves. Meaning they are laying on the floor.
  4. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    The bulb itself could be corroded, if it has even minor cracks in it I would replace it,
    also is the fuel filter inside the tank still attached?
  5. Maico490

    Maico490 LawnSite Member
    Messages: 5

    Hi everyone I'm a newbie having come here with an ignition problem on a Kawasaki FH420V fitted to a scag zero turn. A bit of searching gave me all the info needed including the equivalent John Deere part no as the dealer is local. Certainly a wealth of info here.
    As regards the primer problem I recently had the same symptoms with a FS450 and 400 trimmer at work. I'm presuming a Zama carb but does it have the primer in the carb or is it remote? First thing is to check all the lines but after that it is most likely the main nozzle check valve.
    The info is here on Zama's site:
    The nozzles are replaceable and only cost about $4.
    I recently posted on a chainsaw site how to press them out and install the new ones. Both the trimmers mentioned are now running fine. I will try to copy the post over as the symptoms match a lot of posts here but time is a bit short at the moment.

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