I have a 1979 maxi II, and I installed a 70cc kstar kit with a hihi head on it, it has a proma gp pipe, and a mikuni vm20 carb. it was running like a beast when i first got it installed,i didnt gps it but i imagine it was topping out around 50mph. ran solid for a week, i tried to go easy on it breaking it in, and i did for the most part... ok but then i was riding and it sounded like it backfired and then it lost power. let it cool off overnight and had a hell of a time starting her the next morning, took a lot of pedaling and then it was running a lil rough and not nearly as fast - still faster than stock though. i took the topend apart and it didnt seize or anything. any ideas? i'm trying to figure this shit out on my own but its hard to troubleshoot. someone suggested the hihi head may create too much compression? is it at all possible the throttle cable has anything to do with it? THANK YOU KINDLY to any and all who give me some advice. much obliged, keep rippin.