The carburetor in an internal combustion engine is used to regulate and maintain the correct mixture of air and fuel in relation to the engine's load. When an internal combustion engine ignites its fuel, it creates a high amount of energy in the form of expanding gas and transfers that energy to its specific purpose. Because an internal combustion engine functions by igniting fuel, the correct combination of air and fuel is necessary to create the proper amount of combustion, just as in a wood-burning stove, the regulation of air is necessary to maintain the desired amount of heat and use of fuel – in this case, wood.
The carburetor performs multiple tasks at the same time. It filters the air intake, calculates the necessary ratio of air to fuel based on the engine's load, and distributes the proper amount of fuel to the air stream feeding the engine. By means of a part called the venturi, the carburetor creates an area of lower pressure than atmospheric pressure – commonly known as a vacuum – and uses that pressure differential to meter the fuel into the engine. The carburetor must be designed to negotiate a number of variables, such as the temperature of both the air and the engine, the changes of acceleration, and the difference between operating with a partly open throttle and a fully open throttle.
In part because of the many complicated functions for which the carburetor is responsible, the automobile carburetor has mostly been replaced with electronic fuel injection. This process started with the addition of electronic components to the carburetor in the early 1980s, which soon led to the widespread replacement of the carburetor. Although the carburetor is a simple device that is much easier to work on than more complicated fuel injection systems, the electronic systems are better able to optimize performance. While the carburetor is capable of performing multiple tasks at the same time, electronic fuel injection systems can divide these subtasks into different systems and create the most efficient system for each particular task.
Because the carburetor is lighter than an electronic fuel injection system, it is still commonly found on motorcycles and other small automobiles. Older cars still contain carburetors, and there is a regular market for new and used carburetors for these vehicles.