Story by Phil

“The Q-jet is the easiest carb to work on and has the best interchange of all GM carbs….”

From the old Carter WCFB the Buick 401 went to the Rochester 4 GC. It was a better carburetor but presented a problem with Buick. Because most Buick owners never floored their cars and the 4 GC used four float chambers the gas in the secondary float bowls would go stale. This gas would varnish up and clog up the rear half of carb.

Then came the Carter AFB. Only two float chambers, both primaries and secondarys share a common float chamber. The AFB had a better throttle response but NO gas mileage.

You guys with the Carter AFBs watch the steel plate between carb and manifold. It will develop holes in it where it blocks exhaust passage. This allows wet exhaust to eat into the carb and bind the throttle shaft. We use to change these plates at the 12000 mile tune up. Because the Rochester 4 GC has a cast iron base they don’t use the steel plate.

Also you fortunate few that have a 425 dual quad set up (1964-1965) watch that front carb. If you never put you foot in it the gas will varnish up. The front carb does not have an idle circuit and they are hard to get. If you never floor it block the fuel line off to it.

First introduced in 1965 on the Chevrolet 396 engine the Quadrajet became GMs carburetor of choice. Refined for 1966 the Buick 425 was the next guinea pig. Because of the small primaries and large secondary the gas mileage was improved over the Carter AFB. Finally we are down to one float chamber. The Q-jet is the easiest carb to work on and has the best interchange of all GM carbs.

I have the Delco master carb book listing all the internal specs for GM carbs from 1962-1985. If you have replaced your carb with a rebuilt and it just doesn’t seem right the rebuilder probally changed something internally. Holly brand remans are known for doing this. This book can give you the proper internal specs i.e. jet size, primary rod size, primary piston and spring size, secondary rod size, secondary rod holder size and more.

There are about five different casting if the Q-jet the choke set up being one of the big ones. Using the correct casting for the engine you can change the internal parts to make it work on different engines.

Phil