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Our Rotax 912ULS has done around 350hrs, regularly serviced, runs on Mogas, and carb balancing completed recently. We have a recent problem with engine cutting at low revs.

Performance on pre-flight check, engine warm, normal: min. idle around 1,600. However, on a recent approach, throttle idle, engine cut. Subsequent test, on the ground, after a flight (so engine hot), had the same result.

Linkage and stops are OK. We’re checking the carb float needles level with fuel, cleaning the jets. We’ll re-check performance with engine warm and hot.

Would appreciate further suggestions for investigation. Engine management system perhaps?
Thanks in advance.
  • Re: Hot engine cuts at idle

    by » 6 years ago


    If you were at idle then you were in the idle circuit in the carb. If the carb sync has been a short time back I would check it again because something may have changed. I would do this first. If you are using gauges for the sync a clogged idle circuit will show up as a high vacuum reading over the unaffected carb. You may also want to pull the idle jet out and take a 16 ga. wire, strip it back about 2"-3" and then pull out 1 strand of the twisted wire and use that 1 strand to rod down through the idle jet. It's a tiny hole. Follow that with some carb cleaner in a spray can and then some high pressure air. Flush some carb cleaner and air through the jet in the carb bowl to.

    There is a slight possibility that you have a heavy float and it's flooding out. You'll know this when you pull the bowl and look at the floats and weigh them.

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


    Thank you said by: Richard Lyon

  • Re: Hot engine cuts at idle

    by » 6 years ago


    Very many thanks, Roger - we'll action this tomorrow.

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