I would like to call on the knowledge and experience of you guys to understand a strange behaviour on my Rotax 503. If this would occured during flight, the result could be detrimental. The 503 sits on a RANS S17. It has about 200 hours. It was recently checked up and all gaskets, jets etc was changed in the carbs, new fuel lines, filters etc. It has been running like clockwork, before and after. Today was a hot day by our standards (30 deg C = 86F), which is really nothing particular elsewhere, but maybe it matters. I had been flying about 2,5 hours, the latest flight about an hour. After landing, and taxying to hangar on low throttle, I wanted to turn the airplane with a burst of throttle. Instead of the usual response, the engine sputtered, almost choked and produced no power. After several failed attempts, I stopped the engine, and tried again after a few minutes. Same behaviour. I stopped it, waited about 30 minutes, -and it worked like it should again! However, I am not happy to go flying with this engine without understanding why this happened, and how it can be avoided.
Have anyone in this forum an idea of the possible causes and mitigation of it?
I am grateful for your thoughts
9333_1_IMG_5102.jpeg (You do not have access to download this file.)
  • Re: Failed response to throttle

    by » 2 years ago


    When was the last time you serviced the carburetors.  What you encountered sounds like a flooded carburetor.  If you were at an idle the engine is not running smoothly.  If your float needles are the least bit dirty, they could possibly not seal completely this causing one (or both) of the carburetors to overfill causing a flooded carb situation.  As soon as you touch the throttle the engine would stumble.  Noting that the engine cleared up with time is also an indication the issue was intermittent.

    My suggestion is to disassemble the carburetors and clean them thoroughly.  If the float needles had the old style red/orange rubber tips, the needles should be changed out to the newer ones with the black tips.  Any Rotax dealer will know which ones to use.

    You should also look at cleaning the air-filter.  A dirty filter can cause over-rich operation and have the same symptoms.

    Hope this helps


    Bob Robertson-Light Engine Services





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