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engine stumble at WOT

in 912 / 914 Technical Questions 7 years ago

  • Re: engine stumble at WOT

    by » 7 years ago

    Did the plugs on one side look different from the plugs on the other side?

    One Liter per minute is a questionable rate.
    Is that just gravity flow or with the AUX pump running.

    The 30gph rating is a typical pump output.
    You should see 30gph at either carb but not at both carbs at the same time. (Not 60gph).
    At WOT, the engine only uses ~5gph total, (2.5gph on each side), so 20-30gph total is a safe overkill value.

    We still do not know if the Right Carb is seeing the same flow.
    This is no time to assume anything is working properly until you prove that it is!

    I will assume that the Electric pump is in series with the Mechanical pump.
    That is, the electrical Pump has to pump through the mechanical pump.
    If the Mechanical pump is blocking the flow, the electric pump is not going to help.

    If you shut down the Electric pump at WOT, What Happens?
    Is the mechanical pump doing its job?

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

    Thank you said by: julian van santen
      
    Report

  • Re: engine stumble at WOT

    by » 7 years ago

    Our Posts crossed.

    We are running out of ideas. (Desperate times call for desperate measures. ;) )
    I suppose the last thing to check which would eliminate the fuel supply would be to see how much fuel actually makes it into each carb.
    A carefully placed container under each carb with the bottom fuel bowls OFF would eliminate everything up to the floats.

    Are we sure the carbs were reassembled properly?

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

      
    Report

  • Re: engine stumble at WOT

    by » 7 years ago

    I ran it just now with the top cowling off on the ground - temp was 105, it was easy to replicate the issue. I felt the fuel line by the left carb it was too hot too touch. On the right side a lot cooler. Is it possible that the fuel is just overheating in that line and carb ?

    It's very heat dependent (the issue)
      
    Report

  • Re: engine stumble at WOT

    by » 7 years ago

    I ran it just now with the top cowling off on the ground - temp was 105, it was easy to replicate the issue. I felt the fuel line by the left carb it was too hot too touch. On the right side a lot cooler. Is it possible that the fuel is just overheating in that line and carb ?

    It's very heat dependent (the issue)
      
    Report

  • Re: engine stumble at WOT

    by » 7 years ago

    You may have hit it!

    100LL will Boil (VaporLock) at 140°F at sea level and 120°F at 11,000 ft.
    "Too Hot To Touch" usually means More Than 130°F.

    Are all your fuel lines in the Red Silicon Fire Sleeving?

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

      
    Report
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