A carburetor is a component of some gasoline-powered internal combustion engines, used to vaporize and mix fuel with air in the correct proportions for proper combustion. Generally, steady speed requires a ratio of 15:1 air to fuel. Richer ratios of 10:1 air to fuel are necessary for starting cold engines.
Air is drawn through the carburetor into the combustion chamber (see diagram) when the piston moves down the cylinder with the inlet valve open. The amount of air is controlled by the throttle flap, which is operated by the gas (accelerator) pedal. When the throttle is closed the idling system, which by-passes the throttle, keeps the engine "ticking over". Another jet, the accelerator pump jet, forces more fuel into the engine when required for acceleration.
Efficient carburetion is essentially for smooth running and efficient engine performance. No carburetor is needed in engines that use fuel injection.