Hey I just got off the phone with VP Race Fuels and was getting the scoop on which fuel to run in the 426. They are telling me the "Motorsports 103 Unleaded" is the stuff that I want. They said they have been working with yamaha and this is the best stuff to run in the bike. If this is not available then they said the Performance Leaded C-12 would be the next choice. Now I know nothing about fuels. I wanted to try a different gas because my bike is running a little rich and don't feel like messing with jetting unless I absolutely have to. I have bad luck when I start messing with things that are running fine. The folks at VP said the bike will run leaner with this fuel. Unfortunetly it souds like a pain in the butt to get. I live here in Corona, CA. and there is only one place to get the 103 they said. I'll get back to you all once I get some and try it, and tell you what the diff. is. Seeya! Chiledog!