I honestly think he may have to jet down. I had to jet down from my current setup on my PWK28 after I got my engine KOR ported and head modded.
If you start out with a small carb and you raise the size, you jet down for the size increase usually because the venturi effect increases the more air the carb flows.
If you do a modification to the breathing system to the right of the carb (think airbox/intake) you generally have to jet up. Likewise if you do a modification to the left of the breathing system (think exhaust) you have to jet up, but if you change the way the engine breathes and processes air internally, you may have to jet down, because now the engine will pull more air across the carb jets, therefore getting more fuel through the same size jet.
So, yeah, for starters, Id jet up, then Id see how it feels. Jet by sound and feel. Everyone on here will tell you to do a plug chop, but Ive learned you can try and read a spark plug all day long, but the bottom line is, if youre making power and you arent detonating, thats a better sign that youre jetted properly. If youre rich, it will break up and youll feel it stutter and not go anywhere. If youre lean youll bog and it wont pull like its supposed to on the main.
Another example of how our machines and jetting can be kinda tricky and odd, lets say youre running a 30mm carb. Ill use Keihin as an example since I know Keihins. Lets say on that 30mm carb youre running a 160 main and a 45 pilot. If you move up to a 32mm carb, in theory youd have to drop that main a size to a 155-158 and youd also have to drop to a 42 pilot and maybe even adjust the needle. Bigger hole, lets more air through. More air across the venturi ports means more fuel through a given jet size.
