Run a Walsh gas tank which is up front by stem and put a 250r or 400ex airbox where tank used to be in the back.

 

Like I said, just a small K&N filter that bolts directly up to the carb. It doesn't take up much space and it would be a lot easier than having to buy a new gas tank and build some air box.

 

I dont kno if you can do a engine swap because the cannondales have chain on the right and brake on left and imported quads have chains on the left and brakes on the right. Unless you plan on turning enigne around it seems kinda funnny though. But the closest thing would be the KTM!

 

Kevin - Turn the motor around? Thats making things a little overly difficult. YOu can do some custom work w/ the swing arm or custom fit another quad's swing arm to fit on the C-dale frame.

airraptor - EFI on the YZF is possible but do you really think it would be worth the $$$$$$$$$$. Another option that a lot of people might like more is using the WR 450F motor since it's electric start and has a kick start as back up. I'd rather just have the kick start because of the lighter wieght but trail riders might like the electric start option. Either way, it'll cost a LOT of money.