Will rejetting be necessary?

[mpm]

Ive got a 2001 400ex with FMF Powercore IV and stock air filter. I bought it used this way and the carb was rejetted for the exhaust. I am about to add a Unifilter to go along with the exhaust and help it breathe better. Do you think it will be necessary to rejet the carb? I know the only way to tell is to plug test it but I kinda would like to know some opinions on what I might could expect that way I can change the filter at a time when the Honda store is open, otherwise I may put it off until Sunday. Please let me know your opinions.

Thanks
Mike

[Steve-o 400EX]

most likely i has been jetted for a filter already, do a plug check and see what u come up with, Its the only way to tell.

[cals400ex]

with you living in texas, a keihin 152 should be plenty. i would just remove the mainjet and make sure a huge one isn't in there. if it is much bigger than a 152, you will just be losing power.