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my 912 uls 100hp has always gotten 5400 on take off, two days ago it started to only go 5000 on take off, will go 5400 or more if on level flight but not on take off, i can get 5200 once i start to climb even tried it landing a few times to see if warming up would make a difference, nothing, . plugs are good, changed the gas, checked the carb floats, checked the carb jets, air filters, checked the pistons in the carbs, turned the prop by hand, compression feels the same.
engine starts the same, stops the same, sounds the same, no new noises or vibrations, muffler has no rattles, the prop is a fixed pitch wooden one.

totally puzzled,
  • Re: low rpms

    by » 10 years ago


    Just a couple more questions. Is the mag drop still fairly equal? Have you done a carb sync with gauges not an electronic device and looked at them for one carb being way out of sync? How old are the plugs and is the gap between .023-.027. I would just do a quick differential compression test just to rule it out completely. It will only take a few minutes. Fuel delivery, how old is the fuel pump and is it a suspect with your problem. Fuel filter clog?
    have you done any other maintenance lately that may need to be double checked?

    While you are at it look for any air intake leaks. It would cause a leaning issue and a reduction in rpm. Look good around the rubber carb intake sockets. Flex them good and see if there are any cracks.

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


  • Re: low rpms

    by » 10 years ago


    it is due for an oil change and i will include the fuel filters. the fuel pressure is the same as before, fuel pump was replaced about 170 hours ago
    mag drop is the same for both about 60 rpm.
    idle is the same, smooth
    checked two plugs, gap was .028, pretty clean less than 50 hours on them.
    will find some with a compression tester and learn how to do that.
    thanks for the suggestions, will keep you informed.

    tony

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