I have a 2000 model 400ex that i just put a 440 bigbore kit and a stage 3 hotcam in. I was told that i would be better off if i ran a race fuel mixture in it so it would not overheat. The guy said since it is an older air cooled model and the thin wall bigbore kit would cause it to overheat. Since high octane fuel burns cooler it would help it from overheating. So i was just wondering if anyone had any ideas on what fuel and what ratio i should use. thankyou