Yesterday, a buddy and I met at a local track in rainy conditions. He has an 02 CRF 450 with a 172 main jet, and my 04 has a 175 main. Both bikes ran fine when we first arrived. We both were low on gas, so we each purchased 1 galon of 100-octane race gas which we added to about a quart of pump gas already our tanks. I noticed a significant performance increase in my bike, particularly on the bottom end. His 02 was barely rideable. It idled fine, but when he cranked the throttle to 1/2 throttle the RPMs surged and fell like it was bouncing off the rev limiter. Any idea what could cause this?