Ok I have a race to go to this weekend. It will be the first race on the new 2008 yz450f. Here is a list of things I am planning to do before the gate drops... 1. Change my rear sproket to a 51T 2. Remove stock exhaust and add a 2007 full Yoshimura system 3. Richen up the pilot and main jets, add fuel screw and turn it 2.5 out 3. Add the quick turn cam throttle system My question is on the jetting. I know I ran a 48/168 on my 07 and it worked wonders. Whats stock jetting and what effect would changing the exhaust sytem have on the stock jetting? Will it richen up the bike or make it leaner? I was thinking about running a 48 pilot and a 170 main. Will this be too rich at sea level? I guess it depends on the stock 08 jetting and how much richer or leaner the Yosh system will make it.