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912 loses 500 rpm during climb

in 912 / 914 Technical Questions 7 years ago

  • Re: 912 loses 500 rpm during climb

    by » 7 years ago

    I replaced all 8 plugs yesterday, put the cowlings back on today, and went flying with a half page of potential tests in hand. Well, it worked perfectly on the takeoff and 5000' climb at 5000 rpm, so I stuffed the list of tests in the side pocket and went soaring. 3.5 hours of idling later, I did a 5000 rpm, 60 knot climb for 3 minutes - still working great. Tomorrow, I'll do a couple takeoffs and climbs to confirm proper operation, but right now, it appears the symptoms were caused by the plugs. I have no idea how, but I'll stick to a 100 hours between changes in the future, probably at every other oil change.
      
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  • Re: 912 loses 500 rpm during climb

    by » 7 years ago

    Hi Eric
    If I understand, most of the time your engine is running at idle (low oil temps, rich mixture). Making an analogy with car engines it’s like a heavy-duty situation and in the case of car the makers recommend that you should reduce by 50% the time or km between oil changes.
    In my opinion you should consider the above and reduce the time between oil changes.
    Take in to consideration that oil and the plugs are one of the cheapest items of the engine maintenance so you should consider changing the oil and filter every 50 hours if using mogas or oil every 25 hours if using avgas and the filter you should go to 50.
    Your engine will thank you and more than that you will be on the safe side.

    Regards
      
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  • Re: 912 loses 500 rpm during climb

    by » 7 years ago

    Bad news - I did a takeoff this afternoon, and the engine ran rough very soon after liftoff, dropping the rpm to about 4400. I heard popping noises and there was a strong smell of gasoline. Reducing the throttle didn't help any, so I continued my turn back to the runway, and landed uneventfully. Two full throttle run-ups on the ramp went to 4800 rpm (normal for the engine), with the engine running smoothly. I could see nothing wrong in the engine compartment.

    I've looked at the data log, and it shows a spread in the EGT readings, suggesting carb/float problems to me. The image is attached.

    I'm totally perplexed, so I'm waiting for my mechanic to call back to see what he thinks is the next step. Still open to suggestions, of course.
    N42EJdatalog-veryroughrunning.JPG (You do not have access to download this file.)
      
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  • Re: 912 loses 500 rpm during climb

    by » 7 years ago

    Hi Eric
    If I understand, most of the time your engine is running at idle (low oil temps, rich mixture). Making an analogy with car engines it’s like a heavy-duty situation and in the case of car the makers recommend that you should reduce by 50% the time or km between oil changes.
    In my opinion you should consider the above and reduce the time between oil changes.
    Take in to consideration that oil and the plugs are one of the cheapest items of the engine maintenance so you should consider changing the oil and filter every 50 hours if using mogas or oil every 25 hours if using avgas and the filter you should go to 50.


    Hi Genival - Thanks for the suggestion, and you might be surprised to learn I already use 50 hour oil changes for Mogas operation, as it is recommended by the Rotax engine manual :^)

    I inquired here and elsewhere about the issues of running the engine in flight at idle, while keeping the oil temperature near 190 deg F. The consensus was the rpm was plenty high enough to avoid the problems low rpm idling can cause, and with normal oil temperatures, it was unlikely to suffer from the idling. I don't recall anyone suggesting the oil be changed more often, nor did my mechanic think more frequent oil changes would be useful. If you know of any studies or reports on prolonged idling, I'd like to know about them. It's an unusual "mission profile", and knowledge is thin on the subject.
      
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  • Re: 912 loses 500 rpm during climb

    by » 7 years ago

    If your rpm dropped that much from full or high rpms you should check the carb float bowls for debris. Check the vent tube coming off the side of the carb and make sure both are connected and they're getting the same pressure input. Both tubes should be coming off on the standard Rotax airbox or you may have them vent tubes in another setup.
    was your electric aux pump on?

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

      
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