Wow guys, take it easy on him. Its the helpful people that make this site what it is right? Peteson i have built several 400EXs and will be glad to help you. First off i have to say i have never heard of a Lexx pipe. Sparks pipes work very well on that bike as we have done alot of testing. Pm me and i will help you with jetting specs. It is something you can handle and is not very hard. Pipe, filter/airbox mod, rev box, and jetting is the 1st step! Then higher compression, Cam, and porting, and away you GOOOOOOOOOOO! :thumbsup: