I know a a lot of you guys have tried this already, but I just got done with it. I did the 2003+ WR model on my 2004 WR450F. Here is what I did, which is what everyone does. What a simple yet God like mod . This takes your fuel squirt time frame from 1.7 seconds (I was running 2) down to 1/2 second by adjusting the AP. This is really just a quick tune mod, since the AP timing screw is already there, its just behind the throttle cover. The throttle response is incredible, there was no more bog coming off the bottom on the higher gears such as 4th and 5th and it reved quiker and got up to speed in no time. I did rejet, I put a 170 main and move my neddle clip down a peg. The bolt is a size 10 with a 24 thread pitch and it is hex head for quick tuneing. I also put silicone (not pictured) on the screw to keep it moving from where I want it and to keep any dirt out of the throttle cover. So there it is, a simple yet very effective mod.