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Rough Running.......need help.

in 912 / 914 Technical Questions 10 years ago
I have a Rotax 912s on a Titan Tornado. I have a vibration that I cannot get rid of and I need some suggestions.

The vibration is the worst from 4800 to 5400 rpm. Full throttle take-off and it is not so bad but when I level off and reduce throttle it gets worse.

I have rebuilt the carbs, replaced carb boots, changed plugs, sync'd the carbs atleast 10 times, sent the prop off for static balance, sent the gearbox to lockwood for re-shim, just completed a dynamic prop balance, replaced motor mounts. None of this has made any difference at all in this vibration. I really do not know what to do next. Any help is appreciated.


this is a youtube video so you can see for yourself the vibration. It is not just visual as you can feel it thru the seat, same with the GPS movement.

https://www.youtube.com/watch?v=Dhas0o2s_2c&list=UUaJg4CalA-Yo5UzgrrsM8Jw&index=1

Thanks,
Travis

  • Re: Rough Running.......need help.

    by » 10 years ago

    This could be engine mounts even though you have new rubber mounts. Kitfox had tubing that went inside the rubber mounts and they were too long. Finally someone figured that out and had a lot of owners trimming those metal tubes to allow more pressure and dampening from the mounts. This may not be the engine.
    Since you have eliminated so much already this may be from the fuselage and not the engine.

    Are you syncing the carbs on the high end around 3500+rpm? If you do it down at the book's 2500 you are too close into the idle and we just don't flow enough air/fuel to make the carb sync very good for the higher rpms.


    Rob,
    Any ideas?

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

      
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  • Re: Rough Running.......need help.

    by » 10 years ago

    I also thought it could be airframe related so I went up to 4k feet and shut off the engine and went thru the various airspeeds and it was smooth as silk.

    The vibration is there thru all rpms but mostly noticed as indicated earlier.
    I have sync'd the carbs at 2500, 3000 and 3500. I have also un sync'd them about 1" and could not notice any differences.

    Running out of ideas.

    Travis
      
    Report

  • Re: Rough Running.......need help.

    by » 10 years ago

    Hello Travis,

    Did you see my thread on this forum? I have problem same as you.

    My motor rough running was at 4500 rpm but is now moved to 2600 rpm after we refit carbs and gearbox.

    I am same as you, I have tested everything many times.

    I have sparking plugs from cylinder 1 that is sometimes black. I try to borrow 2 carbs to swap with mine.

    If I fix my motor I tell you what was problem, can you tell me yours if fixed to help me also?

    Thank you,

    Grzeg
      
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  • Re: Rough Running.......need help.

    by » 10 years ago

    For some reason I think my issue is in the carbs. But I have had them apart 4 times for cleaning and no changes any of those times. I will let you know if I get this figured out.

    Travis
      
    Report

  • Re: Rough Running.......need help.

    by » 10 years ago

    For some reason I think my issue is in the carbs. But I have had them apart 4 times for cleaning and no changes any of those times. I will let you know if I get this figured out.

    Travis


    Hi,
    On the carbs ,have you changed any parts during these 4 cleanings ?

    How far did you dis-assemble , all parts out or partial ? possible diaphragm out of place if blown out by pressured air ?

    Have they been rebuilt with the rebuild kit ? Who did the work ?

    I need to reread the post, but I was thinking of the exhaust sytem too , for a place to inspect for vibration source, cracks in mounting hardware, springs ? ? I am not familiar with the airframe.
      
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