hey all, a friend has a 2001 400ex. he just installed a FMF Power Core 4 slip on pipe. sounds great and added some snap but now hes experiencing some breakup at the mid to higher RPMs.
what should he bump the jets up to to compensate for it breathing better now?
i dont know whats in there stock. the altitude is within a few hundred feet of sealevel. no other mods except the pipe.

thanks in advance for your help.

 

I'd try a 152 and/or a 155. It more than likely has a 148 in it now.