I just got a 2004 450 EXC a few weeks ago and I love it. I know a lot of guys are putting the JD Jetting kit in their bikes before they even ride them. I was lucky enough to meet someone during my first ride on the bike who had another solution. He helped me drop the clip 2 position (started at 3rd from top, ended at 5 from top). If you make no changes, you'll notice that your headpipe will start to turn blue. Dropping the clip didn't make a noticeable difference in the bike's performance, but the pipe stopped turning blue on me.