HI I bought a nice WR450 in mostly stock condition. Seller said it was stock tho he was second owner. I verified that the throttle stop was shortened and the pee pee was out of the exhaust entirely. On my first ride I felt it had pretty good "go" until about two thirds through the rev range where the power and pull flattened off quite noticeably in each gear. Is this a trait of a stock WR450 ? Looking at dyno charts on thumpertalk the HP does flatten after 7000 or so and the torque goes south much earlier than that even. I then did the grey wire only and the difference was chalk and cheese. The flattening out vanished and the bike pulled hard all the way to the limiter. No other problems except that while the bike had popped on decel a bit before the grey wire, it now popped, cracked like crazy after grey wire. (even between gear changes it barked) Scared of leanness, I took it in to Yam and had him do GYTR AIS delete for backfiring and if lean any leaness would be adressed in the jetting changes he would do with the GYTR kit. I also had him fit FMF Ti powercore slip-on thinking it would loosen up the top a bit. I got on afterwards and was a bit dissapointed. My rip through the top 1/3 RPM range has disappeared and the flatness was there again. No more backfiring or popping though. The midrange is impressive. More than before. It either stands up hard in first or second or digs a trench if you lay on the tank. I know that this is where you really want the power but just when you expect things to really get going it just flattens out again on top. There is no real bogging, or any other other flat spots. It starts instantly and idles well. If you wick it hard from idle it will cut out, but when riding in real life i cannot ever forsee doing this. Yam warned me this happens when you do GYTR jetting. Its just not a problem to me though. What he did on the jetting is as follows: He left everything stock except two turns out on the fuel screw- he called it an air screw ? and changed the needle with clip in position 4 for the GYTR one with clip in position 4. Believing the bike was stock, we both expected to find the stock non adjustable needle but rather found an adjustable needle in there, with clip in position 4 as well. He mumbled something about this adjustable needle being supplied with the bike when new. Shouldn't the main have been changed with the needle change ? Any ideas on why my new found top end 'go' got up and went ? Appreciate any comments. Skin.