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912 Fuel line question

in 912 / 914 Technical Questions 6 years ago
This fuel line is on a KitFox with a 912 engine and he experienced an engine quitting at full throttle whomever was working with him thought it was a carb sync issue (which I disagree with since it was running wide open)
I think it may have been the fuel line collapsing? Any thoughts?
912Fuel.jpg (You do not have access to download this file.)

  • Re: 912 Fuel line question

    by » 6 years ago

    What’s the set up like? Is there an electric fuel pump or just the mechanical one?
    I have no particular knowledge how soft the tube may be but how blocked must this fuel line be so the suction can actually make it collapse? Have you double checked that the fuel flows freely from tank to the mechanical fuel pump. How about the vents of the tank, all open and clean?
    If the ID of the fuel tube was too small (impossible to tell from the picture) one may consider the appearance of a small jet inside the tube at high fuel flows. That’s pretty nasty when it happens.
    Do you happen to know how the engine quit? Sudden death or stuttering until dead?
      
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  • Re: 912 Fuel line question

    by » 6 years ago

    The engine quitting isn't a carb sync issue, but could be a fuel delivery issue. Usually even if there is a fuel restriction the engine just looses rpm and doesn't just quit. If the engine shut down like you flipped a switch I would think electrical. If it stumbled for a while like it was running out of gas I would think fuel delivery. Which means it could be a clogged fuel filter, clogged fuel pump, clogged banjo bolts. You can use some carb sync gauges to help diagnose. Leave no stone un-turned and start with the easiest and most common cause first. How was the mag drop? Does it do this on subsequent runs on the ground?

    p.s.
    Personally I would swap out that poly fuel hose for real fuel hose and put it in fire sleeve.

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

      
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  • Re: 912 Fuel line question

    by » 6 years ago

    Its a high wing Kitfox, so no aux fuel pump. The tank vents are clear, I.D. Of the hose looks correct. Filters are clean.
    We are going to replace with “real” fuel line and fire sleeve it. Haven’t had a chance to ground run yet.
    It was wide open and then completely quit, so seems fuel starved, but still need to check everything else.
      
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  • Re: 912 Fuel line question

    by » 6 years ago

    As long as you are willing to do it correctly...

    Auxiliary Electric fuel pumps and Fuel Return Lines are required items in the installation of the 912 engine.
    View this Thread...

    https://www.rotax-owner.com/en/rotax-forum/3-4-stroke-technical-questions/6329-mandatory-fuel-return-line

    It has been reported that when the original German Installation manual was translated into English, "Required" in German was mis-translated to "Recommended" in English.
    As stated in the Manuals, "... the original text in German language shall prevail."

    Required or Not, it is a Darn Good Idea!

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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