The carburetor mixes air with fuel so that it burns more easily in the engine. A vacuum caused when your car's pistons make their downward stroke pulls air into the carburetor. The mixture of gasoline and air is regulated according to engine speed. With higher engine speeds, more gas is sent to the carburetor. This is called a 'rich' air and fuel mixture. If your car is cruising or idling, it needs less fuel, or what's known as a 'lean' air and fuel mix. If your car isn't getting the kind of mileage it should be, it could be an indication of a carburetor malfunction. Other potential indicators of carburetor problems are hard starting, rough idling, stalling, engine misfiring, or dark exhaust smoke. Most newer cars are equipped with fuel injection rather than a carburetor. You'll find carburetors on many cars more than a few years old, especially those with larger engines. Contact a qualified auto mechanic in your area for more information on carburetors.