Other than RPM drop, does it run consistently in th low and middle range? If the RPM is not steady, there is a leak somewhere. Double check the two bolts holding the carb to the crankcase, and the cap screws on the carb.

Did you get a chance to take out the cylinder and see if there are blow-by signs on the wall? Does the engine run very hot (hard to touch)?


In a recent flight, the high RPM droped considerably on my DL50 and the compression was almost gone. It turned out the ring was rotating on the piston and worn excessively. A pair of new piston and ring fixed the problem.