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I built an rv-12 with a 912ULS. I've run it on the ground and balanced carbs/set idle

yesterday did the first run ignition check and got a 1000 rpm drop and rough running engine with high EGTs

pulled plugs and cylinder 1 and 2 had BOTH plugs fouled and cylinder 3 and 4 plugs were normal.

Plan on replacing the 4 fouled plugs and try again.

Please advise

 

Alan

N603NH Rv-12

  • Re: first runup to 4000rpm on new 912ULS

    by » 3 months ago


    Hmmmm! Just speculating;

    Choke's are fully open?

    Air filters in good condition?

    Throttle cables - a weak point in Rotax engine control - do they give consistent movement throughout range (ie binding at any point)

    "I've run it on the ground and balanced carbs/set idle".  Prolonged ground runs may result in sub optimal combustion leading to fouled plugs. 4000 RPM is not a full power condition (where any tendency to "foul" plugs is likely to be burnt off).

    Fouled plugs could impact on larger than expected RPM drops.

    Try swapping plugs around, rather than replacing. Your "normal" plugs will either continue to deliver clean electrodes or foul. If foul the problem is not the plugs.

    Check that all plug caps are fitting securely.

    High EGT's are usually an indication of  a "lean"  mixture - a contraindicator for fouling.

    What sort of exhaust system are you using? (any potential restriction?)

    Is this a new engine? If not how many hours?

     


  • Re: first runup to 4000rpm on new 912ULS

    by » 3 months ago


    brand new engine

    gets were normal on both a and b


  • Re: first runup to 4000rpm on new 912ULS

    by » 3 months ago


    new plugs made no difference

    when A turned off got a 1000 rpm drop

    when b turned off get a 30 rpm drop

    Alan


  • Re: first runup to 4000rpm on new 912ULS

    by » 3 months ago


    Swap the A and B ignition module connector plugs and repeat, determine if the problem moves to module B.

    you’ve checked the ignition switch wiring and grounding yes?


  • Re: first runup to 4000rpm on new 912ULS

    by » 3 months ago


    will recheck the grounding

    I have another ignition module and plan on swapping it out and see what happens

    Alan


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