Yea used to do mini tractor pulls did a lot of work on flathead single cylinder kohler motors. karts are somewhat new, always been around em but never built one. I've just recently gotten the bright idea to build an ohv so its all a learning process all over again. Any help would be greatly appreciated.
2.750" is usually a safe size. If you try to go bigger than that you MAY hit the aluminum.
You also have to be concerned about how much room there is between the bore and the push rod chamber or the oil pasage.
If you go too big there isn't enough room for the head gasket to seal.
You also have to be concerned about cylinder stability if you get it too thin. You loose consistent ring seal.