Freshening Up Your ’68-’80 Corvette’s Quadrajet

Rochester Rebuild

Andy Bolig May 1, 2002 0 Comment(s)

Step By Step

Obviously, the first step is removing the carb. We noticed that the bolts had several washers under them. Since the intake has blind threads for the bolts, often the bolts will bottom out before the carb is actually tight. Make sure your bolts are either originals or they are the proper length. Also, when removing the fuel filter, having the proper tools will prevent damage. The wrench on the right is designed to hold the filter nut so it doesn’t damage the body of the carb. Always use a tubing wrench to prevent rounding off the fittings of the fuel lines.

There are nine bolts holding the top of the carburetor. Don’t forget the two inside the primary circuit opening.

Next, remove the holder for the secondary metering rods and the metering rods.

Using a small punch, drive the pump-lever pin in just enough so the pump lever can be removed. Also, check the operation of the vacuum-break assembly with a hand-held vacuum pump before disassembly.

Check that the power piston is operating properly before removing the top of the carburetor. Put a screwdriver through the opening in the top of the carb and push LIGHTLY to make sure the spring is operating.

With the top removed, you can easily see the power piston and the pump-plunger stem.

Pull the power piston along with the metering rods.

Pull the float and needle-seat assembly. When unscrewing the needle seat, be careful not to let the screwdriver slip and damage the seat.

Here, Chris is pointing out the idle-air bleed. A smaller hole here will help an engine with a longer-duration camshaft (280-plus) idle better.

Remove the choke assembly. Note that there is a small tube between the carb body and choke body. This is to allow vacuum to pull heated air through the heat riser from the intake to heat the choke coil. Did you ever think that the choke adjustment housing could be the source of a vacuum leak?

Here, Chris points out the power piston stop. Under most conditions, you DON’T want to adjust this stop. If you do move it, be sure to count the turns so you can turn it back. Lowering it will give you less fuel; raising it will increase the fuel to your engine.

Remove the pump-discharge ball retainer and ball.

Now you can remove the base of the carburetor and remove the idle screws from the base.

The Rochester carbs use lead inserts to seal several passages between the bowl and base. Chris likes to take a small hammer and very gently tap the lead to help reseat it into the passage. This helps prevent small leaks. At this point we soaked the parts in cleaner in preparation for the rebuild.

The serial number for the carburetor (ours was 17058204) is stamped into the body of the carb. This number will dictate the settings such as float level, vacuum-break adjustment, and idle screw turns as indicated in the rebuild kit. We got our kit (PN 2-5798A) from NAPA Auto Parts.

Install the needle seat (being careful not to damage it), the pump-discharge check ball and retainer, and the primary main metering jets (if they were removed).

Be sure to install all of the cavity inserts. For race applications, these are not necessary; but on the street, they help absorb heat.

Install the base to the body using the appropriate gasket.

Install the phenolic spacer, primary piston spring and piston, along with the metering rods.

Install the choke assembly.

The kits will work for several models of carbs, so make sure to use the proper gaskets. Notice the difference in the elongated holes of the unused gasket. Install the proper gasket over the power piston and pump-plunger stem. Don’t forget the plunger spring.

Install the bowl cover, and be sure to use all of the screws.

Install the rods for the choke and pump. If you use an electric choke, do not use the gasket for the choke cover, or the choke spring will not be grounded.

The secondary metering rods and their holder are installed next.

The screws holding the bowl cover were over-tightened at one time and the housing was deformed, causing the secondaries to stick. Chris filed the housing slightly where the interference existed.

Install the vacuum-break assembly. The kit will include the specifics for adjustment, and changes can be made with an Allen wrench and a screwdriver.

Install a new filter (PN GF471), making sure it faces the right direction. Install it wrong and you’ll have no fuel to the carburetor. Be sure not to over-tighten the filter nut.

No one would dream of rebuilding a carb and then using an old gasket, but what about the PCV? Have you checked to see if it’s operating properly?

When they’re running good, they’re hard to beat. When they’re running bad, all you want to do is beat them with a hammer.

With the introduction of the shark-body-style Corvette, Chevrolet also introduced a new carburetor into the Corvette line—the Rochester Quadrajet. This carb was used on the small-blocks and the L36-option 427. The L71 and L68 427s still used three Holley two-barrel carburetors. There were some variations over the years, the most dramatic being in 1981 (earlier for California cars) when the carburetor was computerized to help meet emissions and fuel-mileage standards. We’ll focus on the ’80-and-earlier style. Note that our carburetor now uses an electric choke assembly, as any ’77-’80 Rochester Quadrajet is able to do, while the pre-’77 carb’s body will not accept it. If your Quadrajet works OK but just needs to be brightened up, you can surround it with shop rags and spray it with carb cleaner, but our carburetor’s idle circuit couldn’t be adjusted—meaning that the primary circuit was leaking, making a teardown inevitable. Follow along as the Corvette Clinic renews our Rochester.

Install the carburetor and start the engine while checking for any fuel leaks. Chris says that a properly built carb should not require more than 3 ½ turns on either of the idle circuit screws. If it requires more, there is still a problem. Once the idle screws are adjusted and the engine is running properly, let the engine cool overnight and then adjust the choke with a cold engine. With that done and everything operating properly, you can rest assured that your Corvette will be sipping fuel correctly for years to come.

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