I have experienced a loss of power and rough running at 4800 rpm on takeoff, pulled the throttle back and the engine smoothed out. Thoroughly cleaned all passages, replaced O-rings, gaskets in both carbs, new needles, floats and brackets, flanges, new fuel pump, fuel and fuel lines. No change. Considered taking up golf in place of flying!!!

But...a friend and mechanic recommended pinching the line from the primer to the left carb suspecting an over-rich condition. That fixed the problem temporarily. Permanent fix was to replace both O-rings on the primer plunger. The O-rings were 27 yrs old (engine was new in 1993). Extra fuel was being introduced to the left carb through the primer line. The Rotax 912ul now runs like new. So be sure to replace O-rings every five years.

Bruce O.
Kitfox III, 1993
Rotax 912ul
Warp drive 3 blade prop