A carburetor (also spelled carburettor or carburetter) is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Venturi effect or Bernoulli's principle or with a Pitot tube in the main metering circuit, though various other components are also used to provide extra fuel or air in specific circumstances.

Since the 1990s, carburetors have been largely replaced by fuel injection for cars and trucks, but carburetors are still used by some small engines (e.g. lawnmowers, generators, and concrete mixers) and motorcycles. In addition, they are still widely used on piston-engine–driven aircraft. Diesel engines have always used fuel injection instead of carburetors, as the compression-based combustion of diesel requires the greater precision and pressure of fuel injection.

The term carburetor is derived from the verb carburet, which means "to combine with carbon", or, in particular, "to enrich a gas by combining it with carbon or hydrocarbons". Thus a carburetor mixes intake air with hydrocarbon-based fuel, such as petrol or autogas (LPG).

The name is spelled carburetor in American English and carburettor in British English. Colloquial abbreviations include carb in the UK and North America or carby in Australia.

Air from the atmosphere enters the carburetor (usually via an air cleaner), has fuel added within the carburetor, passes into the inlet manifold, then through the inlet valve(s), and finally into the combustion chamber. Most engines use a single carburetor shared among all of the cylinders, though some high-performance engines historically had multiple carburetors.

The simplest carburetors work on Bernoulli's principle: the static pressure of the intake air at the fuel entry point, which can be in a tube which is constant diameter, reduces at higher speeds compared with the pressure in the float chamber which is vented to ambient air pressure, with the pressure difference then forcing more fuel into the airstream. If the tube is a constant diameter the configuration is slightly simpler than in the diagram shown to the above right Cross-section schematic.

In most cases (except for the accelerator pump), the driver pressing the throttle pedal does not directly increase the fuel entering the engine. Instead, the airflow through the carburetor increases, which in turn increases the amount of fuel drawn into the intake mixture.

Bernoulli's Principle applies (apart from friction and viscosity and turbulence etc.) to both the air and the fuel, so that the pressure reduction in the air flow tends to be proportional to the square of the intake airspeed, and the fuel in the main jets will obtain a speed as the square root of the pressure reduction so the two will be proportional to each other. If the pressure reduction is taken as from a reduction of area along the air flow rather than from ambient pressure to the fuel entry point the effect can be described as the Venturi effect, but that is simply a derivation from the Bernoulli principle at two positions.