just after the main jet size on a 138....
main jet
Re: main jet
0.051" if I remember rightly, simply referred to as 51.
Re: main jet
Yep, factory 51's for most greys, with 50's for humpies.
327 Chev EK wagon, original EK ute for Number 1 Daughter, an FB sedan meth monster project and a BB/MD grey motored FED.