i have a 07 yz450f just shimmed the thing an rode it for 2 hours an it ran fine. got it out the next day an started it , rode about 100 ft. an it died . l kicked it about 100 time ,drug it with a truck no luck. went home an check the timing an it was way off. so ,we retimed the bike an rode it but it seems down on power an back fires and is hard to start. if you look at the cams the intake cam has more angle on it than the exhaust . i m 100 percent sure that the motor is set to tdc an i m on the rite timing marks. only thing i can think of is the intake cam slipped . anyone ???????