I have an AW 60cc engine (airworld from Germany) that I bought second hand. Initially it was running poorly - when I advanced the throttle quickly it dies and when I advanced it slowly it will continue to run but at a very low RPM. I tried adjusting the needles but this did not seem to help much. Then one day it started running well. Got a few flights with it, but now its back to running with about 1/2 the thrust it previoulsy had. Any ideas as to the problem?

John