I have an 01' 426 that i had jetted at dyno jet, and installed a baja designs lighting coil. the bike has run awesome for many years. I made a stupid mistake and loaned the bike to a good friend. he said he stalled the bike and couldn't get it started again. i got it back and put a new plug in it and got it started but it ran like crap. at top end it would sputter and when i let off the gas it would pop. I've rebuilt the carb and saw nothing it could have been. Could it be ignition? timing? weak spark? thanks for all your help.