24 mph is really low, sometimes on a unmodified engine the smaller sprocket keeps the engine from reaching the needed rpm to produce the maximum horse power. The guys that reach the higher speeds have a good bit of improvements done to theirs. Just as a example I have a straight plug head on one of my 48cc engines that has been shaved .040, ports cleaned up and the piston skirt trimmed to clear the intake port at tdc, it will do 30 plus on flat roads with a 44 tooth rear sprocket. I have another engine that has a angle plug head with a nice squish band with porting and piston trimmed that has reached 32 mph on the same bike.