Who's the Engine Expert??? I put the White Brothers slip on the good ol' 07 YZ 450. The power down low is lots better and feels better overall. The only thing that I need help figuring out is why the bike doesn't rev out like it should. It was like this before. I rode a 08 after mine and the 08 has way more top end power. The 07 used to rip up top and lately its not. It pulls great down low but as soon as it hits the mid through the top its not as powerful as it used to be. Its better to lugg it around then it is to rip it up high. My two guesses is that it needs a valve adjustment and/or the jetting is not right. Can anyone give me some Ideas???