Hi fishman, Welcome here,we try to help. I have no Colt experience but there are a few basic things that can be looked at. Does it throw the belt whe bit is being used or when you disengage the cutter. If it comes off when you disengage it it is most likely the belt guide at either the cutter pulley or the engine pulley is allowing the belt to jump off. If the belt comes off when using it it is either an alignment problem or the belt is just worn out. Best way to work on them is drain the oil and fuel and either tip it on its side or if you can chain block it safely stand it vertically. This way you can get at everything and get a better idea of what is going on.