Rotax 503 throttle problem


Active Member
Dec 17, 2021
So I was really hoping to do some taxi testing today on my Phantom with the new pitot/static system being recently completed. However, after I started the engine and climbed in, while it had been idling normally, the engine inexplicably increased in rpm. I checked the throttle, thinking I had bumped it, but it was full back at idle. I cycled the throttle to see if the cable was moving freely, which it was, and the engine went to full throttle and stayed there. After shutting down, quickly, I removed the airbreather to look for obstructions and found none. So being somewhat unfamiliar with these engines, is this a normal piston position for the throttle on a 503 with a Bing 54 carb at idle? This seems to be as low as the piston can travel. I'm more than a little confused on this. The only other thing I can think of is if the boot attachment to the engine has a significant air leak in it. Any other ideas?


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