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Rotax 503 engine problems


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l have a 503 in my Maxair drifter which has done 90 hrs since rebuild on certain days l lose 800 rpms ,one it will run fine all day next time it has full power 6800 at start up about 1/2hr flight it loses power back to 6000 rpm then other days that's all l can get out of it from start up ,put new plugs ,changed air cleaners check exhaust for cracks, both mags work ,clean fuel and filter ,even changed taco ,any body got any suggestions other than use it for boat anchor.


cheers Geoff.



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Carbs are prone to fuel flow issues:


The rubber tip float needle valves can become non sealing leading to float overflow (look for signs of fuel venting the float hoses)


with this you get too rich mixture at the full throttle end


The crankcase pulse fuel pump may need checking see that its getting the pulses and both lines are not getting air bubbles into them


with this you get leaning out of one carb


I liked my 503s, the model is in demand again as nothing better is available new



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