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912UL Engine vibration on throttle back

in 912 / 914 Technical Questions 12 years ago

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi Paul,

    I'm not ruling out the carbs completely and it would need a good Rotax tech to go through the carbs top to bottom. I'm not a fan of wood props these days. In the old days they were every where and prop material wasn't as varied as it is today which gives so many better choices. When was the last time you checked the torque on the prop bolts? They need to be torqued every 25 hrs. I find them loose on peoples planes all the time. Plus wood props along with others should have a dynamic balance. Wood props should even get a static. The newer composite props like Sensenich the static isn't as important because of the newer techniques in manufacturing and balancing at the factory, but a dynamic balance can always help any prop.

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

      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Thanks for the suggestions. Engine mounts are those that came from the factory. I can't reproduce the vibe on the ground and can run it up pretty fast just holding with the brakes. I will try a prop balance. Strange that it happens at altitude mostly. Other thing I thought of trying is different position of the circlip on the needle, perhaps richer? My installation doesn't have an airbox (no room) and it is summer right now and particularly hot. If hot air is being drawn into the carbs could that be an issue?

    Cheers

    Paul
      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Are your summers hot and dry or humid and has it changed from one to the other? It can change the torque on your wood prop hub bolts and they could loosen a tad from being in a dry climate turned from a humid one. It could be the prop loading and unloading in flight. Just one more thing to rule out.

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

      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    I took the prop off the other day and inspected it and the bolts, re-torqued again, I moved the prop position on the hub thinking pulses vs prop position may make a diff but if anything made it worse. Bolts torqued to specs on reinstall. I am only mm's away from ordering a new prop as don't have anyway to borrow one. Your suggestion of it being the prop loading/ unloading makes sense as I can reproduce the vibe in a shallow dive without changing throttle setting.

    Paul
      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi,
    Just my 2 cents.

    I did not see questioning the fuel itself or the fuel system:

    1. vapor lock issues? return line?
    2. bad quality of fuel
    3. water in the fuel?

    Jan
      
    Report
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