Come on now EZGO nothing is ruined on this site , just a bigger challenge. Brandy, where are you located-what state? I have to admit the design leaves a little to be desired but it is fixable. Too damn cold for a go kart right now, at least in Illinois. Send me the sprocket and if you have the key send that too but it is not needed, just nice to compare how distorted the shaft keyway is. Put the sprocket on the shaft before you send it to me and include a piece of wood the exact length from the shaft end to the outside edge of the sprocket when it is on the shaft. This way I know how long to make the insert.
Reading Jon2523 it sounds like it is a 6mm bolt. Go to you local hardware store and buy an M6 bolt and the thread is 1.0. See if that fits in the hole in that shaft and let me know. When you buy the hex head bolt get it at least 30mm to 40mm long You want a lot of threads goin into the shaft. The reason it is falling out is there is not enough bolt length going into it to hold it on.
My address, look it up on the web site--Max-Torque, Ltd.