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912ULS runs very rough above 4200 RPM

in 912 / 914 Technical Questions 11 years ago
912ULS, Runs very rough above 4200rpm, the enrichener smooths it out.

Mag checks at 3500 are fine

Starts ok, idles fine

450 hours, been out of service for a year, I recently did carb rebuild among other things

  • Re: 912ULS runs very rough above 4200 RPM

    by » 11 years ago

    the ignition is fine so as the carbs are the last to be touched you should go back and look at them:
    -do the slides move easily?
    -are the atomizer ports clear all the way to the main and pilot jets?
    -Did you dunk the carbs in cleaner? If so is the "button" on top of the carb cap leaking? (its actually a paper-type gasket so it does not like being immersed in cleaner). the cap needs to be sealed so the auto-mixture can function: The cap area above the diaphragm is routed to venturi so if the cap is leaking the slide will not be pulled upwards with increasing vacuum.
    Rob
      
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  • Re: 912ULS runs very rough above 4200 RPM

    by » 11 years ago

    Thank you Rob, I am going to pull the carbs off, now I have a few things to look for. Yes I did dunk the carb caps. How would I re-seal them if they are leaking?
      
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  • Re: 912ULS runs very rough above 4200 RPM

    by » 11 years ago

    2 part epoxy works well. Don't use silicon in fuel system!
    Thank you said by: Robert Hirschfield
      
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  • Re: 912ULS runs very rough above 4200 RPM

    by » 11 years ago

    Took carbs off, checked all ports, everything is open, slides are operating properly as vacuum increases - I watched them operate. Even when the engine is breaking up at high rpm the slides remain open and steady. Installed soft start modules, new plugs, cleaned fuel system, new fuel. Problem persists. The engine starts running rough at about 4000 rpm. Mag check at 4000 is normal. At higher throttle settings engine breaks up almost violently and rpm decreases.

    Help.
      
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  • Re: 912ULS runs very rough above 4200 RPM

    by » 11 years ago

    Have you run it up with a set of vacuum gauges on them? Have you done a differentail compression test?
    Was this like this before the carb rebuild?

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

      
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