I've got an 85 moto4 yfm 200 that I just acquired. It didn't run but now does. It starts and idles good. If you try to give it throttle it seems to bog and backfire and sputter. After a while the exhaust pipe gets really hot and is almost glowing. So far to get it running I replaced the choke cable and cleaned out the fuel tank and pit ****, replaced the muffler with one that had a spark arrestor. Any advise would be appreciated.