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Still relatively new to the Rotax family of 912ULS engines, I am learning on the go. This morning I was up for an early flight, temps around 21C with humidity feeling like 25C. I had been up for about 30 minutes at 3000 feet when all of a sudden the engine sputtered for a couple of seconds and then returned to normal operation. I use 91 octane mogas in the engine and there was at least 10 gal. of fuel in each tank. The tanks were filled by myself 2 days ago. The plane is always hangared. So my question is this. What could possible have caused the engine to sputter like it did after being in the air for 30 minutes. Could it be a vapour lock and if so, how does one prevent this from happening again? If not a vapour lock what else might it be? I always buy my mogas from the same busy gas station so I don't believe the quality of the fuel should be an issue. I did not do a water check of the fuel this a.m. as I was up yesterday for about 1.2 hours with no issues. Any thoughts or suggestions would be appreciated. The engine tach time is 345 hr. and I have put approx. 55 hr. on it in the last 3 months.
  • Re: Engine sputter

    by » 9 years ago


    Terry
    had the same thing happen to me...I suspect it was carb ice.
    Mike

    Thank you said by:

  • Re: Engine sputter

    by » 9 years ago


    Mike that is something I hadn't considered but certainly with the humidity it could have been the cause. I am used to flying fuel injected big engine aircraft that aren't affected by carb ice so I will pay closer attention to this in future. I can only hope that it was carb ice but still can't rule out vapour lock or something lurking in the background. Thx. for your thoughts. Anyone else care to chime in?
    Terry

  • Re: Engine sputter

    by » 9 years ago


    Hi Terry

    Carb icing all day long.

    Mark

    Thank you said by:

  • Re: Engine sputter

    by » 8 years ago


    Hi Terry
    I have had the same problem during take off on my rotax-914. The engine sputtering for a few second during full throttle. I shut off one of the electrics fuel pump and lower the rpm from 5000 rpm to 4500 rpm the engine run smooth again, I had about 350 hrs on this engine I still don't know cause for this but guessing to be fuel starvation or flooding carb. My fuel return line going back to the gasculator not the tank. I still not find out the real problem.
    somgiat.

  • Re: Engine sputter

    by » 8 years ago


    You have a different problem but you are correct, you have a fuel problem.
    First: you really should not run a 914 fuel return line to the gascolator; what you are doing is taking away the fuel pressure regulators ability to regulate: it must have a resistance-free path to return the fuel to the tank. If the fuel pumps are before (upstream) from the gascolator you REALLY should not route the return line to the gascolator as the return line is now going to a pressurized location!




    as you can see if you restrict the return fuel flow the regulator cannot regulate.
    - You may have a leaking float bowl, this is the most common cause of hesitation/loss of power at boost.
    - or the float bowl has been distorted by over-tightening the bolt. This bends the float pins outwards causing the floats to rub and hang up on the bowls. see attached pdf
    -Least likely: your fuel pressure regulator may need to be adjusted. see attached
    floatbowlovertorque2.pdf (You do not have access to download this file.)
    FuelPressureAdjustment.pdf (You do not have access to download this file.)
    FuelPressureRegulator.jpg (You do not have access to download this file.)

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