For anyone interested in migrating a Q-Jet to a different application OR using an original Q-Jet on a modified original application:
A gentleman by the name of Doug Roe wrote a book on various Rochester carburetors, including the Q-Jet.
A gentleman by the name of Cliff Ruggles wrote a book on modifying Q-jets.
Mr. Roe was the design engineer on the Q-Jet in the early 1960's. I think his book was written around 1970.
Mr. Ruggles is "Mr. Quadrajet" to the current car hobby. I think the first issue of his book came out about 2010. There has been a lot of changes from 1970 to 2010.
I started reading carburetor literature and working on carburetors in 1959. Since then, I have acquired, and read (mostly) hundreds of books on carbs. Of them all, Cliff's is absolutely number 1 when it comes to being "user friendly". It is not as technical as Doug's book, but it does not require a degree in higher mathematics to understand everything.
The book is paperback, and not expensive; anyone working on one of these should own the book!
As to the secondary operation, Buckshot is spot on; however, the secondaries may also be tuned with choke pull-offs with a different vacuum orifice. And while for exceptionally radical engines, the spring tension MAY be adjusted, we have found for less than full race applications the original setting on the tension works best. Tuning of the secondaries is better accomplished by: (A) change in secondary rods, (B) change in secondary hanger, (C) change in CPO vacuum orifice.
Also remember when rebuilding a Q-Jet ALWAYS replace both the secondary cam and the secondary spring!
Jon
