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912 UL wont rev past 4k

in General Tech Discussion 9 years ago
Ok guys- need your help. Was flying my Kitfox yesterday, ran perfectly, landed on a USFS strip, spent about 20 minutes, went to leave and could not get it to rev past 4000 rpm. It runs smooth from idle to 4000, mag drop with 50 rpm either side, but when you push in the throttle it's starts running rough after 4000 and hits a wall. Cleaned jets, checked floats and needles, throttles open evenly, cleaned gascolator, checked plugs, even checked the lifters and valves. Changed fuel pump also. I am out of ideas- any thoughts would be appreciated as the only way to get out of this strip is to fly it out- no roads to it. Thanks- Scott

  • Re: 912 UL wont rev past 4k

    by » 9 years ago

    Hi Scott,

    A couple of questions.

    When you pulled the carb bowls and checked the gascolator were they clean?

    Just thinking outloud here for any possibilities.
    Do you have another inline filter or an inline fuel pump that may be slowing the fuel flow? Do the pistons (slides) in the carb move up and down freely? Could be a clog at a banjo bolt? I would check the Banjo bolts and if you have access to an air supply disconnect a fuel line way back by the tank someplace, disconnect the fuel hoses at the carbs and blow through the system and see if you have free flowing air or if there is some back pressure? This sure sounds like a fuel flow restriction issue.

    p.s.
    Do you happen to have a friend named Jay?

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: 912 UL wont rev past 4k

    by » 9 years ago

    First thought is a fuel system blockage. Filter
    Do you have an auxiliary electric fuel pump ? If you do I would disconnect fuel lines at carbs and turn it on to verify carbs getting unrestricted fuel.
    These are what comes to mind first off , you did allot of investigation already, but a second check might find the smoking gun.
      
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  • Re: 912 UL wont rev past 4k

    by » 9 years ago

    Turns out it was the carbs- specifically a ripped diaphragm on the slide. Thank you Roger and Kevin for the quick responses and input, I really appreciate it.

    Scott
      
    Report

  • Re: 912 UL wont rev past 4k

    by » 9 years ago

    Hi Scott,

    A couple of questions.

    When you pulled the carb bowls and checked the gascolator were they clean?

    Just thinking outloud here for any possibilities.
    Do you have another inline filter or an inline fuel pump that may be slowing the fuel flow? Do the pistons (slides) in the carb move up and down freely? Could be a clog at a banjo bolt? I would check the Banjo bolts and if you have access to an air supply disconnect a fuel line way back by the tank someplace, disconnect the fuel hoses at the carbs and blow through the system and see if you have free flowing air or if there is some back pressure? This sure sounds like a fuel flow restriction issue.

    p.s.
    Do you happen to have a friend named Jay?



    Yes I do. Jay loaned me his carbs.
      
    Report

  • Re: 912 UL wont rev past 4k

    by » 9 years ago

    Turns out it was the carbs- specifically a ripped diaphragm on the slide. Thank you Roger and Kevin for the quick responses and input, I really appreciate it.

    Scott


    Thats the firefighter coming out of us, used to a fast response !
      
    Report
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