Cavebull - the early 2G series with the short taper needles from 3/4 to 1 1/2 turns. The later 2G series (post-1968 smog emission) with the long taper needles from 1 1/2 to 3 1/2 turns.
Carter, Stromberg, and Rochester all went to a long taper screw with the implementation of smog emission. The longer taper gave a much finer adjustment; thus the difference in adjusment specifications. Since we don't do Holleys, I cannot comment on them.
Jon.
