Ok... I have a 04 yz450. I recently posted a thread entitled "yz450 revving problem". Let me sum it up for you. The bike ran great for the first week I had it. Left it sitting for a few days after my last ride and came back and tried riding it again but it was popping and back firing. It also was sputtering when I got on the gas towards mid to high rpms. Idles great... no problem there. So I cleaned the carb a little bit. Checked the air filter and it was all fine. So i went a got about 5 gallons of 93 octane and added a whole bottle of octane boost to it and changed out the gas for the new higher octane gas... still popping and backfiring bad, and sputtering and popping while i am on the gas. I pulled the plug it was black as night so I changed it and it ran for about 1.5 hours and it basically ran like it was before the problems started. I left it for a couple more days came back today and It was worse than it was the first time. Popping and backfiring really bad and sputtering and popping while i was won the gas... idle still perfect. I pull that plug that only had at most maybe 2 hours on it... again totally black! Whats my problem? Is it the gas with the octane boost or what? I mean i don't think the fuel mixture could have all of a sudden got that bad because I never adjusted it. PLEASE HELP!