Myself and friends spent a frustrating afternoon with an OS61FX, that just would not run properly. Now we have tuned many an engine over the years, and after doing all the usual inspections and fixes, the motor still did not cooperate. It would run well at first from a cold start, but as it came up to temp', the RPMs would fall off dramatically. Idle was unreliable below 3200 RPM. The fuel is fresh...even tried a separate new jug..cool power 15%, the fuel system is leak free, and no air bubbles are in the line. Prior to our "tuning project", the owner had the usual OS61FX air leak problem, where the brass plug on the remote needle assy would loosen and back out enough to admit air, and so lean runs surely had occurred before we began playing with it. When cold, the motor felt like it had compression, but after running up to temp, the motor could be turned over without much of any compression resistance being felt. We have our suspicions, but rather than put words in your mouth...we'll ask the question.....whats your opinion as to diagnosing and correcting this problem?