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Intermittent skip

in 912 / 914 Technical Questions 5 years ago
2016 912 with 130 hours. Recent annual with fuel filter, oil, and spark plugs.

Yesterday first problem ever. While warming up on a 60 degree day the power suddenly dropped from 2500 to 2000 rpm . Add to that there is a skip that happens every 5 minutes yes or so that past for 10-20 seconds before going away.

Also noticed this during power down on final. The skip caused a vibration that was gone with a power up to 3000 rpm.

I realize this is random But I'm surprised with such low hours. Any advice greatly appreciated.

  • Re: Intermittent skip

    by » 5 years ago

    I would drop the float bowls and look for debris, also pull the idle jet and check for (green) corrosion.
      
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  • Re: Intermittent skip

    by » 5 years ago

    Checked bowls. Clean as a whistle.
    Set to 4000 rpm, the rpm wandered from 3950 to 4050 and man in wandered from 23.2 to 25.2.

    I also noticed one spark circuit runs rougher than the other. I did just have them replaced. Is that typical?

    However, this prior underperformance was at about 40 degrees F and high humidity. Could this be a carb ice issue? How are the carbs heated?
      
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  • Re: Intermittent skip

    by » 5 years ago

    What is the gap? Make sure the center insulators did not get broken while gapping. Make sure the slide moves easily (not sticking). And last I took Roger Lee's suggestion and set my gap's to .023" which got rid of an intermittent misfire on my engine also. The carbs can be heated several ways, isn't it in your POH? What kind of aircraft's this on?
      
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  • Re: Intermittent skip

    by » 5 years ago

    Many times some slight rpm wander comes from the aircraft throttle setup and can be fairly normal. Yes some are pretty solid. The analog gauges don't show wander near as much as the new digital stuff on the market. They are just sensitive.
    Type of plane?
    This could be several things and without more info it's just a shot in the dark. Some ideas below.
    What is the mag drop check doing? Normal mag drop can be 30-100 rpm and it depends if you're using an analog gauge or a sensitive digital one that reads in finer increments. . I have seen more, but not normal.
    To start trouble shooting: Have you checked all the plug gaps? What is the plug gap? The NGK plugs right out of the box are gapped at .030. Gap them down if need be. Are the carbs synced? Carbs aren't normally heated. Some that have individual filters on each carb get heat from under the cowl. You aren't getting carb ice at idle or just above. You may want to unscrew each spark plug cap and trim the plug wire back about 3/8", apply a dab of dielectric grease and screw the cap back on.


    Maybe as we get more info we can narrow down a cause.

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

      
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  • Re: Intermittent skip

    by » 5 years ago

    It's a 2016 TL3000 with 130 hours. Carbs are synced.

    Garmin Touch Digital Display. Mag drop is 50-100

    I'm certainly not a Powerplant mechanic but I thought the reason Rotax don't have manual carb heat is because they are heated full time.

    She was running pretty rough on final the other day with power down. Mechanic thinks the slightly above freezing temps with high humidity a factor.

    Checked bowls and did a runup today and it seems better although it still runs a little rougher on one mag compared to the other.
      
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