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Stihl FS 45 Trimmer - Primer Problem

Discussion in 'Mechanic and Repair' started by Hurricane_777, May 20, 2009.

  1. Hurricane_777

    Hurricane_777 LawnSite Member
    Messages: 3

    Hello all, was hoping you could help.

    Recently replaced the primer bulb on my Stihl trimmer (old one had cracked and was leaking). I replaced the fuel that was leftover from last season (unfortunately!), have pulled the fuel lines and blew them clean, also blew the feed lines on the carb / primer clean as well. The darn thing still will not prime (no fule in the primer bulb).

    I'm at my wit's end with this thing. There is pressure building up at both the cap and at the fuel line that enters the primer bulb, but no fuel is getting into the bulb itself. I pulled the tank and checked the filter and that appears okay as well. I figured it was a bad gas problem, but short of pulling the carb apart to clean I think I've done everything I could.

    Any suggestions????

  2. rpaquet

    rpaquet LawnSite Member
    Messages: 10

    My Stihl BG75 blower problem sounds similar. I very carefully rebuilt the carby last year, but didn't solve the problem.

    When I press the bulb, air bubbles go into the tank. When I release the bulb, no fuel is being pulled into the carby.

    I will be eagerly monitoring you post for good info.
  3. Breezmeister

    Breezmeister LawnSite Bronze Member
    Male, from South Jersey
    Messages: 1,784

    When you push on the primer, you are pulling fuel from the tank, threw the carb and then back into the tank. I would start simple,check the fuel line for any kinks, then on to replacing the fuel filter in the tank. If that does nothing form you, then it's on to the carb. You can try to clean it, with carb cleaner with the little straw, but you have to take it apart to do that, if that works for you great. If not, you can get a kit to rebuild it. Personally, I don't bother rebuilding carbs any more, less aggravation to put a new one on.

    Good Luck
  4. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Messages: 2,249

    Are sure you didn't happen to reverse the two lines to the carb. If you did, the return line to the tank from the carb will not likely be in the fuel and will only pull air from the tank to the carb. If the lines are properly installed and the fuel filter has free flow, about the only thing that will prevent the primer bulb from operating is a faulty check valve in the portion of the carb immediately below the primer bulb. This check valve can be easily damaged if you blow high pressure air through this portion of the carb.

  5. mowerknower

    mowerknower LawnSite Senior Member
    Messages: 766

    The check valve in the carb is stuck, I normally put the hole carb in my high temp parts cleaner and it will free it up and work like new. Otherwise you will probalby have to replace the carb. Should only be about 60 bucks.
  6. Hurricane_777

    Hurricane_777 LawnSite Member
    Messages: 3

    Thanks so much for the responses guys!!!!

    I did pickup a carb rebuild kit ($12) and was going to go that route, but I'll try soaking the check valve first and see where that gets me. The potential for damage part makes me a bit nervous, as I did (gasp) attempt to blow it out using a drinking straw and some deep breaths. Hopefully I didn't screw it up.

    I did check the fuel lines and they are routed okay, the filter appears to be clear / clean as well.

    I'll keep everyone posted, thanks again!

    STIHL GUY LawnSite Fanatic
    from CT
    Messages: 5,226

    can you get a carb rebuild kit at any hardware store??
  8. Hurricane_777

    Hurricane_777 LawnSite Member
    Messages: 3

    Not sure, Went through my local Stihl dealer. It's a Zama carb, so they're probably more widely available.

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