After riding the '99 WR with the lid on for a while and stock jetting (168 main, DXM needle 4th clip, 45 pilot-2 turns out) I got curious and whipped the seat and you guessed it! The airbox lid. I rejettted with a 170 main/DXM 6th clip/45 pilot-4 turns out. It was quicker but ran a little funny in the midrange and popped when backed off from 3/4 to full throttle. Then I ordered the DXL (richer) needle and finally 3 weeks later I recieved it! THE RESULTS I installed it (5th clip) and MAN does this thing have some midrange snap now! It runs silky smooth in the midrange and even has a little more top end- but still dies a little on approx 1/8 throttle. I guess I'll have to try the 48 pilot and settle for more low-end grunt as well! In short, ripping off the airbox lid, then rejeting a WR makes a very worthwhile power difference! I say more than any aftermarket pipe. It also runs a cleaner pipe and uses no more fuel than stock.