yoshimura jet

[Yoshi400ex]

i have a 01 400ex yoshimura slip on k&n filter and prefilter closed airbox lid..what jets should i be running?...

[trailburner]

155 main in the summer & maybe a 160 in the winter......that should be the only jet you should have to change........but allways do a plug check no matter how good the moter feels..

[redroost85]

I have the same as you, but I jetted with the lid off. I know it sounds crazy, but I have a 165 main in right now. I know I will have to go down to about a 162 in the summer, but the 165 is working right now.:)