Whats the best performance mod for the Z400. The only thing that Ive done to it is put a prodesign adapter with the foam filter. Want to get some more kick out of the girl

 

I would say as the single best mod go with a pipe but for others look at what I replied for CP1s post.

later
Supestar

 

Yup, It's not too expensive and it will make a very noticable difference. Pipe and jet, and I would also take the airbox lid off while you're at it... thats if you dont get reeeeal muddy when you ride, if so just keep the lid on, no reason to take any risk.