To tell the truth the engine is hopeless.Firstly the carb is made of aluminium and when the crankcase heats up the carb temperatures also rises. It pushes the fuel back to the fuel tank.If im not wrong this process makes the engine run lean and it overheats .

best bet is to change the carb from a os or a novarossi [ carbs that is half aluminium and composite ]to keep the temps down on the carb to get a stable idle and constant performance.