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rough Running 912 midrange rpm

in 912 / 914 Technical Questions 9 years ago
My 912 is running rough at about 42 to 4900 Rpm in the cold weather. We have meticulously balanced the carbs to no avail.we lowered the circlip to the bottom botch as the spark plugs swem to be more white than tan colored. The prop has been checked and appears fine. Any ideas?? Thx

  • Re: rough Running 912 midrange rpm

    by » 9 years ago

    What rpm are you sinking your carbs at? The prop was checked for pitch and track between all blades?
    Is this rpm vibration always repeatable or off and on? Have you checked your throttle cables on the ground and slowly opened it up and watched to make sure each carb is opening the same. There could be a bad spot in your linkage causing an unbalance it this point.

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

      
    Report

  • Re: rough Running 912 midrange rpm

    by » 9 years ago

    Yes we are checking carb sink through the entire range and it's perfect even vacuum throughout. It seems much worse the colder the oat.It is a newer carbon fiber prop and has been set properly. The plugs seem a bit lean more white than brown. the egt is approx 60 degrees higher on the rt bank At 52 5200 but at 3000 they are matched! Chasing my tail
      
    Report

  • Re: rough Running 912 midrange rpm

    by » 9 years ago

    All sounds good. Many Rotax engines have an rpm range that they don't run as smooth as other rpm areas. EGT spreads can vary from 0F-80F depending on your rpm. If you watch these as you change rpm you can watch them come together and also spread apart.

    All you may need is a dynamic prop balance. If it is new I would certainly do that.

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

      
    Report

  • Re: rough Running 912 midrange rpm

    by » 9 years ago

    I could see having to balance the prop if the problem persisted in the warm weather but in temps
    above say 50 it seems much smoother. Just seems to be running lean in the cold weather. Besides setting the carb clips lower or changing the main jet is there anything else I can do to richen it up? It has the stock jetting. Thx
      
    Report

  • Re: rough Running 912 midrange rpm

    by » 9 years ago

    Are your carb needle clips in the third notch and are they both the same?

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

      
    Report
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