| The purpose of a carburetor is to mix air with | | | | When a car is not running, there is no vacuum to |
| fuel for use in an internal combustion engine. | | | | draw in the fuel. To remedy this, a butterfly valve |
| Although the carburetor has largely been | | | | known as a choke is closed to create enough |
| supplanted by fuel injection in the automotive | | | | vacuum in the carburetor in order to draw in fuel. |
| world, it is still very commonly used in a number | | | | Once the engine is running, the choke is opened |
| of applications. Nearly all cars before the mid | | | | and the carburetor performs normally. The choke |
| 1980s use carburetor systems, and some | | | | can also be partially closed to enrich the mixture, |
| specialized automotive applications still do. Smaller | | | | meaning that is fuel-rich. This is done during cold |
| engines, such as those used in lawnmowers, | | | | starts to help warm the engine up. Another |
| ATV's, outboard motors, chainsaws and other | | | | butterfly valve controls how much air and fuel |
| small equipment are almost always carbureted. | | | | flows into the engine. This is called the throttle. |
| A carburetor works in the following steps. First, | | | | The wider the throttle is open, the greater the |
| fuel is pumped into a float bowl, where a float | | | | airflow through the carburetor. The greater the |
| regulates the amount of fuel drawn into the | | | | airflow, the more fuel is drawn in, and ultimately, |
| carburetor. Adjusting the level of the float | | | | the higher the engine power output. |
| increases or decreases the fuel flow into the | | | | Smaller carburetors normally have a single barrel, |
| carburetor, which ultimately raises or lowers the | | | | however, larger carburetors can have multiple |
| air-fuel ratio, known as the mixture. Fuel is drawn | | | | barrels like 4 barrel carburetors or 2 barrel |
| into the carburetor barrel by what is known as | | | | carburetors. Many high performance cars featured |
| the 'venturi' effect. As air enters the carburetor, it | | | | a four-barrel carburetor, allowing a large quantity |
| passes trough a constriction which increases the | | | | of air/fuel to be drawn into the engine, increasing |
| velocity of the air. Flowing at a higher velocity, the | | | | the power output of the engine. Generally, all |
| air is at a lower pressure, creating a vacuum | | | | carburetors follow a similar model, although some |
| which draws fuel into the carburetor barrel. As | | | | may vary, for example, some carburetor designs |
| the fuel enters, it evaporates and mixes with the | | | | do not have chokes, instead using a different |
| incoming air. This is then drawn into the intake | | | | system. |
| manifold and into the engine. | | | | |