How to Set a Quadrajet Float Levelby Chris Stevenson
The Rochester Quadrajet, or Q-jet, was a carburetor on many GM vehicles from the mid-1960s to the late 1980s. Its primary front barrels look no different than other carburetors and work well for low and mid-range speeds. The secondary barrels on the Quadrajet have very large openings and throttle plates, which produce a hefty dose of gas upon acceleration. This kind of brute horsepower has made the Quadrajet carburetor popular on the racing circuit and among high performance enthusiasts. The float on the Quadrajet must be set to the right specifications to allow for proper fuel delivery.
Put the vehicle in park or neutral, depending on your transmission type. Set the emergency brake and raise the hood. Remove the air cleaner housing top nut by hand or by socket and pull the housing off. Use a fuel line wrench to loosen the fuel line to the carburetor inlet. Pull the vacuum hoses from the carburetor ports, or use a screwdriver or pliers to loosen the hose clamps.
Tape the hoses and mark them with a pen for their location reference. Unsnap the throttle cable linkage at the ball socket. Unhook the throttle return spring. Use a fuel line wrench to loosen and remove the steel vacuum line fitting on the back of the carburetor. If you have a heat tube attached to the choke mechanism, pull it free with pliers. Use a socket to remove the four base bolts on the carburetor. Lift the carburetor off the manifold, taking care to not disturb the lower gasket.
Take the carburetor to a bench and set it bottom side down. Use a screwdriver to remove the small screw that holds down the metering rod hanger. It has a Y shape. Use pliers to unhook the choke that attaches the top carburetor plate to the bottom plate. Use a hammer and punch to drive the accelerator pump arm pin in just enough to remove the pump arm.
Remove the nine screws on the top plate of the carburetor (air horn), using a screwdriver. Pull the air horn off. Pull out the two metering rods and set them aside. Remove the small float bowl shield gasket. Use a turkey baster to remove any gasoline in the float bowl and dispose of it in a certified container. Look at the float and its pivot arm. A needle seat sits under the pivot arm.
Keep the float pivot down with one finger while you push down very gently on the needle below it with another finger. The float will rise as though floating in liquid. Keep that position. Use your other hand to place a float bowl gauge on the other end of the float (at the top) and measure the distance from the top of the float to the edge of the gasket surface of the casing. Refer to your owner's manual for the correct height in inches.
Adjust the float up or down by bending the small float support arms (tangs) on both sides, using a pair of needle nose pliers. After the adjustment, put your fingers on the pivot and needle and check the measurement again. Place the small gasket shield back on the air horn top. Install the two metering rods down into their small barrels and attach the small support arm that holds them in position.
Push the retaining end of the (metering rod) support arm down into its seat with a screwdriver. It has a spring underneath it, so push it until it snaps in position. Place the top case of the carburetor onto the base, making sure the accelerator pump arm comes up through the hole. Insert the nine top case screws in the top case and tighten them with a screwdriver. Reconnect the accelerator pump rod and choke linkage rod, in the reverse fashion you removed them.
Place the metering rod hanger into its seat and tighten its mounting screw. Place the carburetor onto the intake manifold. Replace the base gasket at this time if it looks deformed or crushed. Assemble the carburetor parts in the reverse order that you removed them.
Refer to your tape marks to find your vacuum line locations. After assembly, reconnect the negative battery cable with a socket and turn the engine over for several seconds to fill up the float bowl. Once the engine starts, refer to your carburetor manual for the correct procedure for idle mixture and speed adjustments.
Items you will need
- Hemera Technologies/AbleStock.com/Getty Images