For combustion to take place in an engine, atomized fuel must mix with air in the optimal ratio for operating conditions and demand. On just about all road going vehicles produced today, computer-controlled fuel injectors spray fuel into the intake air stream, but for most of automotive history carburetors blended fuel and air for combustion. Fuel injection began supplanting carburetors in the 1970s so cars and trucks could meet stricter emissions standards.

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The central part of a carburetor is the “barrel” formed by the air horn at the top, the venturi in the center, and a throttle plate at the base. There can be one, two, or four barrels. The barrel is adjacent to a fuel reservoir called the float bowl. A carburetor functions because of the pressure differential caused by atmospheric pressure and engine vacuum, and another pressure differential created by the taper in the venturi.

The pressure differential draws air through the carburetor. As air moves through the venturi its velocity increases and the pressure drops, which draws fuel from the float bowl through an orifice and into the airstream, where it atomizes. The throttle plate is connected to the accelerator pedal via cable or mechanical linkage. When the pedal is depressed, the throttle plate begins to open, additional passages are exposed and more fuel is added for the increased airflow. As the plate opens further, fuel begins to flow from a nozzle at the center of the venturi. Some vehicles also have a small booster venturi within the primary venturi.

A richer mixture is needed at wide open throttle, and this is provided either by a spring loaded power valve or with metering rods in the main jets. The accelerator pump provides a quick shot of fuel when the throttle is opened rapidly. A choke plate restricts airflow when the engine is cold, to provide a richer air/fuel mixture. The choke can be controlled manually, electrically, or by engine heat. An engine-mounted mechanical pump supplies fuel through an inlet valve to the float bowl. The float rises with the incoming fuel, and when a predetermined level is reached, a valve seats in the inlet, shutting off fuel flow.

Four barrel carburetors generally operate only on the front two barrels for idle, cruise and low speed operation. The other two barrels, commonly known as the secondaries, open either mechanically or via vacuum diaphragm when additional air and fuel, and more power is needed. The carburetor is mounted on an intake manifold, where the air/fuel mixture vaporizes and is distributed to each cylinder. Whatever your carburetor repair needs, we can help, with new and remanufactured carburetors for select applications as well as a large selection of rebuild kits and replacement parts like accelerator pumps, float assemblies, choke pull-offs and more.

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4.8 of 5
Throttle Cable 73 Camaro
Needs thinner seal at firewall.
KPosted by Keith (West Seneca, NY) /
1973 Chevy Camaro
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