Depends on what type of motorcycle(actually carb) you are dealing with Aron.
Most commonly they are in millimeters or inches and even(rarely) in numbered
drill sizes and even guages(i've never seen the latter myself). You're
correct for most japaneses motorcycle carbs though. A jet marked 175 is a
1.75mm orrifice and a jet marked 45 has a .45mm hole in it. For SAE a jet
marked 70 has a .070" hole. But on that rare occassion you might find a jet
marked 50 and it have a .070"(or 1.78mm) hole denoting it is a drill size. No
matter what they say or are marked it is always best to check them with a
reliable system of your own as manufacturer tolerances are terible(especially
Keihen and aftermarket companies for CV jets in the harley industry). When at
the shop I used to use a mic. and verify my drill bits for the best fit. I
have minus- guages(pin gauges) nowadays and scrutinize them much closer and
also use a small engraver to mark them what they actually are. At the track I
use my drill bit sets and verify them with a cheap digital vernier caliper
(good thing about these pieces are they will convert from metric to sae for
you at the push of a button and are very inexpensive).
TD
> I remember.............that somewhere I read that motorcycle jet
> sizes relate to their hole diameter in millimeters, i.e. a #140 main
> jet is a 1.40 mm hole. Can anyone confirm or deny this? I can't find
> any references on the net... -Aron-
|