How to Adjust a Carter 2BBL Carburetor

by Michelle Schaefer
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The Carter two-barrel carburetor was used on millions of domestic cars and trucks for several decades. The carburetor, like any precision machine, requires periodic adjustments to keep it working at its peak performance. Making the proper adjustments ensures the engine can run at its proper speed without stalling and still maintain optimum fuel economy. Adjusting a Carter carburetor requires only a handful of simple tools.

Step 1

Start the vehicle and apply the parking brake. Spray starting fluid around the base of the carburetor and intake manifold. Listen for a change in engine operation or rpm. Any change in operation or rpm indicates a vacuum leak. Shut the engine off and repair any vacuum leaks before attempting to adjust the carburetor.

Step 2

Adjust the accelerator pump linkage. Install the pump connector link in the outer hole of the pump arm with the ends extending away from the counter-shaft arm. Back out the throttle lever set screw until the throttle valves seat in the carburetor bores. Hold a straightedge across the top of the dust cover boss at the pump arm. The flat on top of the pump arm should be parallel to the straightedge. Adjust the arm by bending the throttle connector rod with a pair of needle nose pliers.

Step 3

Adjust the metering rods. Back out the throttle lever set screw to allow the throttle valves to seat in the bores of the carburetor and loosen the metering rod arm clamp screw. Press down on the vacuum meter link until the metering rods bottom in the carburetor body casting. Hold the rods in the downward piston and with the throttle rods seated, revolve the metering rod arm until the finger on the the arm contacts the lip of the vacuum meter link. Hold in place and carefully tighten the clamp screw.

Step 4

Adjust the fast idle. Loosen the choke lever clamp screw on the choke shaft. Insert a .010-inch feeler gauge between the lip of the fast idle cam the the boss of the flange casting. Hold the choke valve tightly closed and take the slack out of the linkage by pressing the choke lever towards the closed position. Hold the choke valve tightly closed and tighten the fast idle adjusting screw until there is .020-inch clearance between the throttle valve and the carburetor bore. Be sure the fast idle adjusting screw is on the high step of the cam when making this adjustment.

Step 5

Adjust the choke unloader. Hold the throttle wide open and measure the clearance between the upper edge of the choke valve and the inner wall of the air horn. Bend the unloader lip on the throttle shaft lever until a clearance of 3/16-inch is achieved.

Step 6

Adjust the dashpot. Close the throttle valves all the way and depress the dashpot diaphragm fully. Adjust the clearance between the dashpot stem and throttle lever to 3/32- to 1/8-inch by bending the dashpot link rod.

Step 7

Adjust the idle air bleed screws. Turn the idle air bleed screws clockwise until they gently seat. Turn both screws out one complete turn each. Start the engine and adjust the air bleed screws until the engine runs smoothly. Ensure each screw is turned out exactly the same amount on each side. Normal adjustment is from 1/4 to 1-3/4 turns on the idle screws.

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