I just recently purchased a new KLX and was wandering what would be the best exauhst modifications for it. Also I would like to know if there are any other mods to improve horsepower and wieght.
you could start with a high flow aftermarket exhaust, like an FMF or Big Gunn or supertrapp, plus a K&N air filter with some custom holes tapped in the air intake box. and if its the same as the DRZ400, which i think it is, theres all kinds of other things you might do.
as for wieght reduction...good luck. i'm sure it can be done.
Do a search in the Thumper section under DRZ400. There are some websites that you can visit. The easiest and cheapest mod would be to rejet and open the airbox. Or try a DynoJet kit. If you want to spend about $400-500 you can buy an aftermarket exhaust and shave off about 15lbs. Another quick fix is to drop down the countershaft sprocket one tooth. I did this and there as a noticeable improvement in low end. I think that next I am going to open air box and then buy a 47t rear sprocket. Good luck.
i just bought a 2003 klx400 and i run a leo vince exhaust, it gives it a lot more go down low and a bit more up top. as far as jetting goes the standard jetting we get on the australian bikes is fine even with aftermarket pipe (165 mainjet).
i am a motorcycle mechanic in austalia, when we get new klx's in they have a restcrictor in the inlet manifold, im not sure wether US ones have the same thing because the austalian version is regestrable.