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High RPM Roughness

in 912 / 914 Technical Questions 12 years ago

  • Re: High RPM Roughness

    by » 12 years ago

    The engine is a 912 ULS with 120 hours. No recent maintenance. I hope to find time this weekend to troubleshoot the problem. I'll start by looking at the plugs, wiring, fuel filter, then carbs. My Rans has a drip bowl under the carbs, so I will need to remove the carbs before I can drop the bowls. Of course I hope to find something simple as the cause! Thanks for everyone's suggestions.
      
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  • Re: High RPM Roughness

    by » 12 years ago

    Many issues are easy, it's just us owners that make them hard to find. ;)

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

      
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  • Re: High RPM Roughness

    by » 12 years ago

    Hi JD

    Do you have a fuel pressure guage fitted and if so was there a drop in pressure. If not have you got the new fuel pump fitted or the
    AC pump.

    If you have the AC pump fitted it could be that the pump is failing.

    Mark
      
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  • Re: High RPM Roughness

    by » 12 years ago

    I have the new fuel pump. Fuel pressure remained constant, electric fuel pump made no difference.
      
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  • Re: High RPM Roughness

    by » 12 years ago

    Got to the airplane this afternoon. Plugs all look good to me, no obvious differences in the plugs. Fuel filter is fine. Removed both carbs, there was a small amount of soft sediment adherent to the bowls of both carbs. Several small floating flecks of soft material were in both bowls. One small fleck in one bowl was firmer but I could pulverize it with my finger tips. All jet passages appear to be open. The idle jets have a very small opening, I can barely see light through them. I guess this is normal.

    Not sure I have found the problem, altho I guess one of the small flecks could have obstructed the main jet.
      
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