rejetting a 400ex

[ReddRacer250ex]

Sup guys im rejetting a carb for a guy's 400ex. He has an aftermarket slipon on it but not sure what it is though, i need to know what jet size to try. Im located around Wheeling WV not sure what the elevation is.

[4TraxRider]

That's not very helpful at all, but if he installed the slipon and/or removeed the airbox lid you will have to jet richer than what it was before the mods.