Funny thing about octane... it's the RESISTANCE to igniting that raises the number. Higher octane does not equal more power. It can actually reduce it. We use higher octane when the compression is so high, or the timing so advanced that premium will pre-ignite. Race fuel is commonly used in high compression motors and because it is very clean and consitent lot-to-lot. I would venture to guess that if you are running stock compression, you will do best with premium unleaded. Further, the high octane stuff usually degrades throttle response a bit. If you want or need to run a higher octane fuel, I recommend Phillips B-35. It is 99 octane unleaded. B-32 is common too, but it is 110 octane (much higher than needed for a standard dirt bike) and is lightly leaded. Now, lead is both poisonous and bad for the environment, and it's only value - besides raising octane - is that it lubricates valve guides in afour-stroke. You don't need 110 and you don't have valve guides, so stick with the B-35 if premium is pinging. An awesome mechanic once told me that the best fuel to use was the lowest octane that would not result in pre-ignition. Your engine will produce the best power and throttle response on that fuel.