A choke is a valve installed in a carburetor that restricts air flow, which enriches the fuel-air mixture when an engine is started. According to Autorized.com, a choke is designed to help engines start more quickly and efficiently when they are cold.
Autorized.com indicates that chokes are considered part of a vehicle's motor transmission system. Traditional chokes function through a vacuum tube, while modern chokes are powered by electricity.
Hemmings reports that gasoline requires heat to vaporize. The rate of vaporization decreases if the outside temperature is colder. At temperatures below freezing, most gasoline-powered engines require an external heat source to start. Heat is introduced to the choke through a tube that draws hot air from the intake manifold. Electric chokes, which were made available in the 1970s, draw heat from a 12-volt element with roughly the same power as a toaster. In the 1970s, many Chrysler vehicles were outfitted with hybrid chokes that drew heat from the intake manifold but relied on an electric element to engage.
According to Hemmings, electronic fuel injection began replacing chokes on most cars in the mid-1980s. While chokes are just as efficient as electronic fuel injection systems, they do require proper adjustment to function reliably.