Hi: Sorry if this question is too repeated, but I couldn't find the specific point that I am looking for. I have a WR400F '00 with the stock pipe and exhaust (that horrible heavy and black iron). The point is that I like this only because is very noiseless, but is too heavy. I am looking for and aftermarket muffler that can be silent and light at once, don't care about power gain and esthetic. I can't find one. Always when you change muffler needs rejetting? The other question is about FMF bomb header pipe. This is lighter than the stock one? This FMF curve also blocks the oil filter cover like the stock one? Thanks for your answer.