I just got my gyt-r aluminum pipe, pro flow k&n kit and a 168 main, and 40 pilot - yz needle is on back order. An experienced mechanic in the area set me up with the parts and with his discount. I have been reading about jetting for awhile, though, and it seems like most recommend a 45 pilot for a yfz 450 mod. I am at about 600 feet. I am more curious about how the pilot jet affects the big picture. I trust this mechanic, just want to know how it all works. Any help appreciated...