Ok, so I have a 2003 yz450, and I have checked the valve specs every 2 months to make sure, but after I realized that the valves were not wearing hardly at all I went about 6 months without checking them. Now my bike is backfiring when i try to start it. It is really hard to start now. do you think it is the valves, I have ridden it consistantly since buying it brand new and only now is it not starting well. I would be surprised if it went so long without needing an adjustment and suddenly wore so much as to affect starting. Whats your opinion??