A carburetor basically consists of an open pipe, a "throat" or "barrel" through which the air passes into the inlet manifold of the engine. The pipe is in the form of a venturi: it narrows in section and then widens again, causing the airflow to increase in speed in the narrowest part. Below the venturi is a butterfly valve called the throttle valve — a rotating disc that can be turned end-on to the airflow, so as to hardly restrict the flow at all, or can be rotated so that it (almost) completely blocks the flow of air. This valve controls the flow of air through the carburetor throat and thus the quantity of air/fuel mixture the system will deliver, thereby regulating engine power and speed. The throttle is connected, usually through a cable or a mechanical linkage of rods and joints or rarely by pneumatic link, to the accelerator pedal on a car or the equivalent control on other vehicles or equipment.

Common Problems

The main problem with a carburetor is dirty fuel. This can cause a too rich or lean condition, meaning there is too much fuel or air to the mixture. The mixture is normally adjusted by one or more needle valves on the carburetor, but dirt can render these adjustments inoperative. To check your car's mixture you will need to use a gas analyzer to test your exhaust gases. This will measure the carbon monoxide, hydrocarbon and oxygen content of your exhaust. During a normal smog inspection the fuel/air mixture is tested and a report is generated. When a tune up is performed the spark plug end insulator can tell you a lean or rich mixture. Brownish grey is the desired color and confirms proper mixture. Black and sooty means the mixture is too rich while white to light grey confirms a lean mixture.

Basic Maintenance

Changing the air filter and fuel filter will keep dirt/debirs from enterning the internal workings of the carburetor.  This should be performed each time you change your spark plugs.  Spraying a carburetor cleaner into your barrels and adding cleaning additive to your gasoline will remove deposits in your jets and in the carburetor itself.

Learn more about carburetors on Wikipedia

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