Help, my son just got the bike . It was hard to kick start would pop start and run great. Decided to check valves , had no clearance on intake valves. took shims out put cams back in and checked again no clearance. Replaced intake valves with o.e.m. lapped valves squirted water in intake, waited checked and no leaks. put it back together. started on 4th kick , ran 1 min. pushed choke in idled fine, gave it throttle and died. Timings right, valves in spec. gets gas and fire. It backfires out of exhaust pipe at about 5 kicks but refuses to start !! Any Ideas please ?

 

Ok I got it figured out finally! The previos owner apparently put a piston and rings in it .Long story short the rings where stuck! Even new pistons need the ring grooves cleaned! The bike runs awesome now