You will have to re-check your engine. It is possible that it's had an overheat at some time that has caused a problem in the fit between the piston and cylinder liner. Possible dirt ingestion could also cause an erosion of the fit. If the fit is not correct, then the compression will be less than it should be, which will require you to lean the engine to get it to run properly. That's the clue...you had to lean it to keep it running.