RE: Zenoah G62 with a 24 " prop???
You are not burning Ethanol in it....are you? Ethanol in the gas is an issue. It burns 30% faster than gasoline and causes a significantly reduced power output. If you burn an ethanol gas mix in your car...as some gasoline stations are giving you...you will see a corresponding drop in your miles per gallon. Interesting, eh? Pay more, and get less...what a world.
There are a number of potential reasons for your G-62 to be seemingly down on power....fuel/oil mix, carb tuning, air bleeding into the carb/crankcase pulse port....etc. I would suggest that you look quite closely at your tuning. The G-62 is a well known, and very successful work horse of an engine, and you should see much better performance than what you are getting.
By the way, I fly my 22 pound GS Aeromaster very well with a G-45. Not gobs of power to spare, but from your dismal description, it will fly rings around your your plane. Not to brag, but rather to demonstrate that there is an issue with your motor.
You may be a bit timid about tuning the needles, and if that is so...try to have an experienced Zenoah friend tune it for you.
You and your G-62 will be well rewarded by your efforts.