Which device mixes fuel and air in older engines?

The device that mixes fuel and air in older engines is a carburetor.

A carburetor uses the pressure drop created by air moving through a narrowed passage to draw liquid fuel into the incoming air stream. Jets and passages meter the fuel, while a throttle plate regulates how much air-fuel mixture enters the engine. The resulting mixture is then drawn into the cylinders and ignited.

Carburetors were standard on many gasoline engines before electronic fuel injection became widespread. They are mechanically straightforward and can operate without electronic sensors or a high-pressure fuel system, but their mixture control is less precise. Cold starting, altitude changes, and rapidly changing engine conditions can all require special enrichment or adjustment.

A carburetor is not the same as a throttle body. A throttle body primarily controls airflow; in a fuel-injected engine, injectors add fuel separately, often near the intake ports or inside the cylinders. A turbocharger, meanwhile, compresses intake air and does not perform the carburetor’s fuel-metering role.