It has been suggested that the 2008 YZ450F standard needle (#NFLR), #165 Main Jet and a #48 Pilot Jet are a good all around pick for the 2008 WR450F. This combination has been suggested, because you can work around all of the parts of the Yamaha AIS kit. Out of the Yamaha AIS kit all you want is the needle in the kit. You don't need the too rich jets and you can make a metal blank off plate out of thin aluminum, buy vacuum hose plugs at the auto parts store and cut the stock WR throttle stop to the YZ specs from the info on Thumper Talk also. The directions for the free mods are on Thumper Talk, so why spend $50 for a carburetor needle. What have I missed in my reasoning?
Spending more money than you need too. And really how much HP do you really gain.