I have had my 02 WR250f for a while now, and i have done most of the free moda and i am very happy with it. But i think its time to move to the next step. I want to change the timing to yz specs, and i want to get ahold of a yz pipe as well. What kind of jetting can I expect to do? bigger main jet? And also if anybody has a YZ pipe they would be willing to let go pleas let me know. Thanks in advance for your responces.

When I changed mine I went from a 170 main to a 175, I changed to an OCFMN needle at the same time as the timing change but you can expect to go 1 or 2 clips richer on your needle and maybe richen the furl screw.

anybody change to yz timing, AND yz pipe? how am i going to need to change the jetting?, do what hakka reccomended?

Yes if you change to YZ timing and install the YZ pipe, you will most likely need to richen your jetting. I am assuming you have also removed the airbox lid and unplugged the gray wire. If not do those mods too. With this setup and a P-38 my current jetting is:

Current conditions: 80's, sea level to 1500 ft

MJ #178
MAJ #200
PJ #42
PAJ #100
Needle OBEKP
Clip 4
Fuel Screw 1 7/8 out
Leak Jet #40
Starter Jet #72