hey guys sorry if this is some where else, did some searching (thumper and google) and all i come up with is decel popping and a/f or timing. i have a 07 yz450f with yoshi slip on and a heavier flywheel, i just did my valve shims, timing seems to be dead on, but i dont have a gun to check.new a/f mix screw, good gass. my bike after shims became a little harder to start, not horrible but its way harder to kick, when i now start it i have to leave the choke on for longer before i turn it of, and here is where im totally lost, my bike wont stop back firing, its like im getting air in or not detonating fuel until its in the exaugsht. Example: drive up and down the street , it will pop excell and decell. 1. did i do bad shims? 2. could that be my cdi going bad? sorry if this is covered, just send me in a good direction, if i don't know by Tuesday she will be seeing the shop .