A carburetor is a metering device which mixes fuel with air in the correct proportions and delivers them to the engine cylinders as a combustible mixture.
The automobile engine's source of fuel for power is gasoline. In liquid form, however, the gasoline is of little use; its energy can be released by combustion, only when combined properly with the correct amount of air and delivered to the cylinder of the engine as a combustible mixture.
The purpose of a carburetor on a gasoline engine is a meter, atomize, and distribute the fuel through-out the air flowing into the engine. All of these functions are designed into the carburetor and are carried out by the carburetor automatically over a wide range of engine operating conditions, such as varying engine speeds, load, and operating temperature.
The carburetor also regulates the amount of air/fuel mixture which flows to the engine. It is this mixture flow regulation which gives the driver control of the engine speed.
Regardless of engine RPM or load the engine encounters, the carburetor must automatically perform its three basic functions.
The automotive carburetor is a very intricate device; however, when studied one phase at a time, the functions of the carburetor are easily understood.
As mentioned above, the three main functions of the carburetor are to meter, atomize, and distribute the fuel.
Good combustion demands a correct mixture ratio between fuel and air, commonly called the air/fuel ratio. Too much fuel results in a "rich" mixture, while too little fuel results in a "lean" mixture. To release all possible energy by combustion, the right amount of fuel must be mixed with a given amount of air. The metering job of the carburetor is to furnish the proper air/fuel ratio for all conditions, so that the engine operation will neither be too lean for power requirements or too rich for economy.
Atomization means breaking the liquid fuel into very small particles so that it can readily vaporize and mix with air. With the fuel broken into small particles, there is more air contact. The more air contact - the better the vaporization.
Atomization is accomplished in two ways: