Hello Guys,

I have a Engine Vibration during MAG Check

Rotax 912 almost new. It has 57 hours. New Spark Plugs ( Denso Iridium Power IXU 24)

When checking Magnetos at 4,000 RPM, put the key in Magneto No1 and it only loose 100 RPM.... The engine feel smooth. Move the key to position No 2, it only loose 150 RPM but I can fill the engine is vibrating.

Move the Key to both magnetos, the vibration goes away. The engine vibration only shows only when testing Magneto No 2

Any advise?


  • Re: Engine Vibration during MAG Check (Rotax 912)

    by » 13 years ago

    Hi Isaac,

    That could be quite normal.
    Turning off one mag or the other could have a little more vibration than the other, but if you haven't done so make sure those carbs are synced and make sure they are done at idle and up to 3500-4000 rpm on the top end. I have seen many use 2500 rpm for their high end carb sync rpm setting. That is too low. It is too close to idle and we don't cruise that low. A rule of thumb is don't do anything if it is within 10% of the low side or 10% of the high side. i.e. a torque wrench set to within 10% of the lowest setting or the highest. Same goes for your carbs)
    Try this next time to prove it to yourself. Sync the carbs at 2500 rpm then run the rpms on up to 3800-4000 and I would bet 98% of the time they will be out of sync. I never sync carbs less than 3500 and will check them up to 4000. This will make your system much smoother.

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

    Thank you said by: Isaac F

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