GM Rochester Quadrajet - Super Chevy Magazine

The first step in any carb rebuild is taking it apart. Remove the nine screws securing the air horn, and then use a small punch to push the accelerator pump pin in towards the air horn so you can remove the accelerator pump arm and rod. After you lift off the air horn, the accelerator pump can be pulled out. Save the spring from beneath it.

The first step in any carb rebuild is taking it apart. Remove the nine screws securing the

There are several good reasons GM chose the Rochester four-barrel "Quadrajet" carburetor to fuel some of the best musclecars ever made. The Q-jet, as it has become known as over the years, is an efficient, simple, and reliable carb that is easy to tune and can make tons of power. The reason a Q-jet is so simple to tune is that it needs very little adjustment to work properly. When equipped on a new car, most of the Q-jet's primary functions were dialed in at the factory so it could work best with the specific engine it was going to fuel. However, since no car has come equipped with a Q-jet for at least 15 years, factory tuning is no longer available and you've got to make that old Q-jet work on your own.

That's where companies like the Carb Shop can help. Although well known for building trick Holley carbs, the Carb Shop is just as adept at tweaking the Q-jet for the street and the track. We stopped in at their Ontario, California, facility and peeked over the shoulder of "Q-jet Boy" Kevin Van Noy as he rebuilt and modified a customer's carb. Check out the tips and tricks he offered, and after arming yourself with one of the Carb Shop's complete Q-Jet rebuild kits you'll feel better about tackling the job yourself-or at least you'll be able to talk to Van Noy and company with a more astute vernacular. When calibrating a Q-jet's fuel curve, the Carb Shop drills and fills some of the factory holes to give your carb the best power and smoothest drivability possible.

A Carb Shop Q-Jet
If you'd rather have a root canal than rebuild your own Q-Jet, the Carb Shop would be happy to do it for you. There are also several tricks and modifications the fuel masters perform on every Q-Jet that would be difficult and expensive for the average-equipped car guy to do. Check out a few of the tricks the Carb Shop is capable of, and decide if you want to DIY or if they can redo your Q.

Removing the power piston comes next. The primary metering rods hang from the power piston, and you should be careful not to bend them when removing the piston.
Removing the power piston comes next. The primary metering rods hang from the power piston
A spring sits under the power piston and can be removed at this stage. If the spring is broken, replace it with the appropriate new spring (available from the Carb Shop).
A spring sits under the power piston and can be removed at this stage. If the spring is br
Using needle-nose pliers, lift the bowl baffle out and put it aside to be reinstalled later.
Using needle-nose pliers, lift the bowl baffle out and put it aside to be reinstalled late

Lift the float hinge up next, using needle-nose pliers. If the stock float is brass or plastic, it should be replaced with a nitrophyl float that will give your carb quicker float response time, and a float that won't sink.
Lift the float hinge up next, using needle-nose pliers. If the stock float is brass or pla
Use a wide, flat-blade screwdriver to loosen the brass seat. Lift it out with pliers.
This is the adjustable part-throttle screw, which determines the lowest position of the metering rods at cruise speed. Remove it next and inspect it for wear. If it's in good shape, it does not require replacement.
This is the adjustable part-throttle screw, which determines the lowest position of the me

Use a wide, flat-blade screwdriver to loosen the accelerator pump check-ball screw as well. Remove it with your trusty needle-nose pliers and then turn the carb upside down so the steel ball falls out. Don't lose it!
Use a wide, flat-blade screwdriver to loosen the accelerator pump check-ball screw as well
Disassemble the outside of the carb next. Remove the fuel fitting and filter. Don't throw away the spring-you'll need it later.
Disassemble the outside of the carb next. Remove the fuel fitting and filter. Don't throw
The next step is to remove the choke assembly. After removing the center screw from the choke housing, use the choke rod to hook the lever and lift it out.
The next step is to remove the choke assembly. After removing the center screw from the ch

Carefully note the orientation of the fast-idle lever and adjuster before removing it. It must be reinstalled in the same position to work properly.
Carefully note the orientation of the fast-idle lever and adjuster before removing it. It
Two or three screws secure the baseplate and need to be removed to take it off. Then slide the steel baffle out of the secondary venturis from the bottom.
Two or three screws secure the baseplate and need to be removed to take it off. Then slide
The Carb Shop uses a heated ultrasonic cleaning tank to soak the Q-Jet clean for 15-20 minutes. You'll want to soak yours in a big can of carb cleaner overnight. Heavy varnish and stubborn crud can be brushed off with a stiff, chemical-resistant plastic brush.
The Carb Shop uses a heated ultrasonic cleaning tank to soak the Q-Jet clean for 15-20 min

Reassembly is done in the reverse order of disassembly. If you replaced the float, bend its hanger so that the top of the float sits approximately 1/4-inch below the top of the main body with the air horn removed. This will give you a rough float level adjustment to start out with. Further tweaking of the float hanger may be needed to get the fuel level correct.
Reassembly is done in the reverse order of disassembly. If you replaced the float, bend it
After replacing the needle and seat, screw the adjustable part-throttle screw all the way down and then back it off two turns. Install the bowl baffle next, and then the power piston spring, piston, and metering rods can go in after it. Reinstall the accelerator pump check ball and screw, then carefully slip the new air horn gasket under the power piston bracket. You're now ready to move to the top.
After replacing the needle and seat, screw the adjustable part-throttle screw all the way
Before bolting the top back on, reassemble the choke housing and lever using the choke rod to hold the lever in place. Don't forget to tighten all the air horn screws, including the two that are in the primary venturi.
Before bolting the top back on, reassemble the choke housing and lever using the choke rod

Use side-cutters to grip and push the accelerator pump arm's pin back in place.
The Carb Shop seals the factory well plugs with super-tough epoxy. This is often a troublesome area of hidden internal leaks, and this cures the problem.
The Carb Shop seals the factory well plugs with super-tough epoxy. This is often a trouble
While it's disassembled, every Carb Shop Q-Jet's baseplate gets resurfaced to make sure it's smooth and flat.
While it's disassembled, every Carb Shop Q-Jet's baseplate gets resurfaced to make sure it

Most old carbs have throttle shafts that are looser than your wallet on date night; the Carb Shop machines the baseplate and installs oil-lite bronze bushings on the primary throttle shaft to tighten it up.
Most old carbs have throttle shafts that are looser than your wallet on date night; the Ca
Here's something the Carb Shop does to make tuning your carb easier: They install a removable plug above the adjustable part-throttle screw to provide easier access for later adjustments.
Here's something the Carb Shop does to make tuning your carb easier: They install a remova
Every one of the Carb Shop' s rebuilt Q-Jets gets bolted onto the Vrbancic Brother's Racing dyno for a full-throttle flogging before it gets shipped to your door. This big-block street Q-jet had no trouble cranking out 490 hp on a mild 454-cid Rat.
Every one of the Carb Shop' s rebuilt Q-Jets gets bolted onto the Vrbancic Brother's Racin