How to Rebuild a Quadrajet Carburetor 850 CFM

The Quadrajet carburetor was made by the Rochester division of General Motors. It was standard equipment on many GM vehicles for over 25 years. The Quadrajet is a four-barrel carburetor with two small primary barrels and two large secondary barrels. It was designed to provide both fuel economy and power. The Quadrajet 850 CFM was the largest Quadrajet carburetor made. Like all carburetors, the Quadrajet 850 CFM is subject to a buildup of deposits, as well as significant wear and tear. These issues can lead to poor performance, lower gas mileage and stress on the engine. A Quadrajet carburetor rebuild consists of a thorough cleaning and replacement of gaskets and broken or damaged parts. Performing the rebuild yourself with a carburetor rebuild kit could save hundreds of dollars.

Instructions

Preparation

1

Disconnect the car battery.

2

Cut several 2- to 4-inch pieces of masking tape and place them within easy reach.

3

Fill a container with carburetor cleaner. The container must be large enough to fit any part of the carburetor. Fill the container to a depth of 1 to 2 inches.

4

Remove the air cleaner and the air cleaner assembly from the top of the carburetor. Remove the wing-nut and disconnect any vacuum hoses, then lift the assembly off the bolt.

5

Label the fuel line, vacuum tubes and choke wires.

Removal

6

Disconnect the fuel line, choke wires, throttle cable and vacuum tubes. Cap or plug the fuel line and vacuum tubes to avoid contamination.

7

Remove the mounting bolts and nuts from the carburetor.

8

Lift the carburetor off the intake manifold and place it on your work surface.

Disassembly

9

Scrape off any remaining pieces of the gasket from the carburetor and intake manifold. Do not allow debris to fall into the intake manifold.

10

Disassemble the carburetor one piece at a time.

11

Remove the small screw between the two secondary air flaps.

12

Remove the bar that was held down by the screw, and the attached metering rods.

13

Remove the accelerator pump lever. Push in the roll pin with a flat punch until the lever releases.

14

Remove all the screws on the top of the carburetor, including the two in the primary barrels. Lift off the top of the carburetor.

15

Remove the power piston retainer to remove the power piston.

16

Turn idle mixture needles clockwise until they stop. Record the number of turns. Remove the idle mixture needles by unscrewing them.

17

Remove the screws on the throttle plate -- it is on the bottom of the carburetor. Separate the throttle plate from the carburetor body.

18

Drill out the rivets or remove the screws holding the choke coil cover.The choke coil cover is the large black disk on the side of the carburetor body.

Cleaning

19

Inspect each part. Replace any broken or damaged parts

20

Clean each part, using carburetor cleaner and a brush to remove all deposits. If necessary, soak the part in the carburetor cleaner and rinse with water.

21

Dry the parts with a towel or compressed air.

Reassembly and Installation

22

Reassemble the carburetor in the reverse order of disassembly.

23

Screw in idle mixture needles gently until they stop. Turn the needles back out the same number of turns that you recorded earlier.

24

Clean the intake manifold with carburetor cleaner.

25

Place the new gasket on the intake manifold.

26

Set the carburetor on the gasket. Line up the mounting holes.

27

Replace the mounting bolts. Hand-tighten all bolts before fully tightening them.

28

Replace the fuel line, vacuum tubes, choke wires and throttle cable.

29

Replace the air filter assembly, and install a new filter element.

30

Reconnect the battery.