Basic Formula for Jettings

[89katana750]

I am pretty sure I saw on here a basic formula for jetting. Something like if you are to be switching to an aftermarket exhaust with pods, what the general size difference would be for the jets.

I am trying to figure out the jetting for my 90'GSXR 750 engine with the GSXR stock exhaust, 89'kat 750 carbs, and the kat 750 air box. The stock jetting for the GSXR is 127.5. But if I have the 36mm carbs from my kat and I am using them on an engine that has 38mm stock, that would mean that my jetting will be smaller than stock 127.5 right? Anyone know the basic formula?

[Anonymous]

i would start with 127.5 and go from there maybe even 125 as far as a formula for figureing jet size ive never found one jsut what make it go vrooooom is the right one

[burke]

the 127.5 sounds like a good start. at worst it would be rich, which is much better than lean. check your plugs after a couple good pulls and see if they are white or if there are little silver spots on it, if so then jet up to like a 135. if they are real black then start to jet down slowly.
good luck!