Hi all, I have an '82 CT70 (purchased new) with a Lifan 110,(4 speed manual) , in it. I runs great, cruises nicely at 40-45, tops out at 55, but can't quite keep up with my son on his new Monkey. So, my plan is to move up to a 140 or 150. My question is, with the bigger engine, can I still use the 420 chain, or should I get a 428, like on my CL90. If so, are CT70 428 rear sprockets hard to come by?