hey guys, recently my 2004 rmz 250 just shut off while riding still kick started and gears still good just could not get it started after it shut off.thats past week felt like kicker was easy to push down and it was smoking a little bit. so I decided tear motor down and rebuild top end, I replaced piston, rings, gaskets and valve seals. put back together timing is perfect has tons of spark brand new air filter oil filter/oil. fresh gas. my buddy checked the valve clearance for me and said intake were .010 and exhaust were .015 if anyone could give me suggestions on why it wont start? only thing i got were few back fires. im thinking the valves need to be shimmed? I reade that intake should be 0.10 - 0.15 and exhaust should be 0.17 - 0.22 (my exhaust valve clearance was 0.15 could that be the problem?) any replies with help would be appreciated thanks.