[vujade]

Im no carb expert by any means... this is just info that I am passing
on that Ive learned from others on the forums...

first off from what I understand, you start by taking the size of your intake
valve (say you have 40 x 37 valves).

so yo take the 40mm valve and subtract 3mm to come to your venturi
size of 37. then you take 37 and multiply by 4.2 to get your main jet size
(37 x 4.2 = 155)

so you would start with a 155 main jet and go from there.
how you get your air jet & idle jet sizing Im not sure...
I do know that the air jet will usually be larger then the main jet
as in (180, 190, 200, etc)