i have a old zenoah 23cc motor about 15 years old i be leave its a G23 marine motor and i think its a 2 port motor anyway i decided to try it out on my cat (ACR42) took the Std carb out put in a 257 race carb from gizmo motors tuned pipe from Bonzi sports length of header pipe and tunded pipe 12.5 inches octura X465 prop the prop diameter is 3/16 bored it out to 1/4 inch fuel mix 20:1 boat runs very well and it accelerates very quickly and not a bad top end speed having a lot of fun the auther thing i have done or added to the motor is put a different water jacket this is from bonzi sports 2 in/ 2 out i think they call it a very cool water jacket