And so far's I'm concerned, "it's not." I never even HEARD the term "dizzy" or "carby" until Al Gore's internet got wound up
So far as the FBO book, that is one "take." His thinking takes a complete turn-around from what I'm used to and what OEM "did" This in part might be why it's all so confusing.
Furthermore, "smog" strategy (emissions control) which occupied CA from 66, and Federal U.S. since 68 has muddied the water, as you have what is
best for mileage
best for all out performance
"best?" for emissions control.
AbodyJoe posted this I believe: