How to Rebuild and Modify Rochester Quadrajet Carburetors

No amount of effort spent on building a custom high-performance Quadrajet carburetor can be successful unless we are working with a correctly rebuilt carburetor. Over the years I've come to hate the work "rebuilt".

Most things I see that are "rebuilt", especially carburetors, were probably better off slam worn-out than after they were finished! This simply comes from lack of knowledge rather than lack of skills.

Armed with accurate and useable information, we can make sure that your Quadrajet carburetor is correctly rebuilt, so it functions as it was originally intended. Working with a unit that is up to par, we can go in and make metering and calibration changes to get the desired and predicted results.

Most Quadrajets have experienced some wear through many years of use and countless heating-up and cooling-down cycles in the engine compartment. This may leave some units in rather poor overall condition. The decision to work on your current unit or select another core should be made after careful disassembly and inspection of the castings.

Before going into specific rebuilding procedures we go over a few of the common problem areas. Once you have inspected the carburetor and decided that it is in suitable condition to rebuild, you can continue on with confidence that the final product works as expected.


BOTTOM PLUGS

The design of the Quadrajet is excellent. There are no places for the main body to leak other than the factory pressed-in bottom plugs. During the machining process it was necessary to access several areas of the mail casting from the bottom side. This mandated sealing them up afterwards. On the bottom rear portion of the main casting there are two large pressed-in plugs. Very early units have brass cup plugs.

The leakage rate for these units is almost 100 percent. Dabbing epoxy over them is similar to cutting your arm off and putting a Band-Aid on it! Over time the glue comes loose and the leakage continues.

A quick test to determine if the bottom plugs are leaking is to invert the casting and apply a soap/water solution to the plugs. Using compressed air and a long tip on the air gun apply high-pressure air in through the main fuel supply passages or pressed-in rear secondary disks.

If leakage is noted, the plugs are relatively easy to pull and re-install coated with epoxy or the casting tapped for custom-made screw in plugs.

Later units made after about 1968 used pressed-in aluminum plugs.

We still see a few of these that leak, but not nearly as often as the early-style brass plugs. The method to install and swage in the aluminum plugs continued to improve through the years of production. It is quite rare to find units made from about 1975 and later that leak.

• Preface
• Introduction
• History
• How Quadrajets work
• Selecting the right carb
• Tools and safety
• Rebuilding the carb
• High-performance modifications
• Edelbrock Q-Jets
• Quadrajet secondary metering rods
• Quadrajet components