Hey guys, I have just fitted a bills muffler to my 2000 wr 400. I have a 42pilot,75 paj, 170 main, 200maj, and an obeln in pos 3. I started off with a 165 main but she did a little bit of backfiring when I nailed it up the street so I swithed to a 170 and that went away. I expected a lot more of a power increase going from the standard pipe to an open race muffler. The bottom end seems ok,easy to start, fairly crisp and grunty, the midrange is a bit smoother but not much stronger. The top end is where i expected things to come alive but I doubt it even goes as well as it did with the stock pipe, only louder. It would pull 4th gear wheelies at about 80kmh without using the clutch, now it need a handfull of clutch and a big yank on the bars to get her up. Prior to fitting the pipe I had a 160 main and the rest is unchanged. I went up ten on the mj as recommended by taffy, jd, yamakaze(thanks guys)when fitting the pipe but I still want more top end. Will I have to go to yz timing to get maximum benefit from the new pipe or are there other jetting issues I need to attend to. thanks for any advice anyone can offer me.