hey, well the 60cc kit has less probs for the engine but i mean the 70 kit is just 30 dollars more and gives sooooooooo much more power! i have one and i blew a crankshaft so i replaced the crank and bearings now it runs sweet and does 62 miles an hour on flat. of coure i have a few mods with the bore kit. well jsut email me for more info. is your engine old or new? like how many miles and what year
-mike