I read an article from the early nineties from Cycle World or some other publication(it was some guys personal Bandit site with great links). They took a b4 and did a few modifications. They had a K&N, a slip on, and a jet kit(Dynojet?). They used the #96 main jets, 3rd position(groove) on the needle, and had the screw 3 turns out. If you google it, you might find it because there was a whole lot there I can't remember. Maybe the link is somewhere in here, try the 400 FAQ's.
Andrew