The Rochester 4-Jet was produced from about 1952 through 1966. Like most other products, they did have "teething" problems. The initial design (1952~1955) had several issues. Beginning approximately 1956 (there was some overlap for different companys) the 4-GC was an excellent carburetor.
Rochester 4-Jets were produced in sizes from approximately 400 CFM to approximately 700 CFM. There is no "average" size.
There would be no significant performance increase in using a Q-Jet on smaller engines (300 CID or less). The real performance advantage with the Q-Jet is on larger engines because of the small primaries, which allows higher air velocity at low RPMS.
The 4-Jet is a more reliable design than the Q-Jet.
DON'T switch to an electric choke if you have an automatic transmission UNLESS you live in in Miami, San Diego, or Honolulu. Fix the hot air choke.
If you should decide to go with the Q-Jet, it will REQUIRE an intake manifold change. The "spread-to-square" adapters are for the seedy used car lots that switch locations after each car sale!
Either, if properly applied and properly rebuilt, are great carbs.
Jon.
