I just bought my 07' yz450 about 3 weeks ago. The guy I bought it from said he has always run VP racing fuel on the stock jetting, bike had a 3 gallon IMS tank full of fuel when I got it. Anyway first ride it ran great with very little popping on decel and started pretty well too. Went out yesterday and filled up the bike with 93 octane pump gas and now it is popping very bad on decel. I tried adjusting the air screw and it helped a little bit along with turning up the idle a bit too but still popping pretty bad. As I said the only thing that has changed is the fuel, can it have this big of affect on the jetting? Power wise the bike ran strong and didn't feel any different than when running the VP. I reviewed the jetting threads and everyone seems to start with fattening up the pilot, I just need to find out what pilot is in it which should be stock.