Gasoline engines rely on either carburetors or fuel injection systems to deliver the correct ratio of fuel and air to the combustion chamber, which powers the engine and allows the car to run. Carburetors are purely mechanical, while fuel injection systems are electrically based. Fuel injection has been around since the 1950s, but was not widely used until the 80s.

The carburetor tried to adapt to the automotive evolution, but as cars began to be equipped with more mechanisms and operating requirements, the carburetor grew more complicated and consisted of five different circuits. The main circuit provided just enough gasoline for cruising without overusing the fuel, while the idle circuit restricted the fuel to provide the minimum required to keep the engine running while idling. The accelerator pump allows extra gas to flow into the engine to reduce the amount of response time from the moment you step on the gas pedal to the engine actually accelerating. There is also a choke, which helps the engine start during cold weather, and a power enrichment circuit to help get a vehicle up a hill or take on a heavy job such as towing a trailer.

The complicated carburetors gradually gave way to throttle body fuel injection systems, which are also known as central or single point fuel injection systems. These were designed to replace carburetors without requiring automakers to redesign engines to accommodate them. When the engines began to change, however, the fuel injection systems did too.

Multi-port, or sequential, systems replaced the throttle body designs. Rather than a single-point fuel injection, the multi-port setup places an injector at each cylinder, which allows for more accurate fuel usage and faster engine responses. The injectors are electronically controlled valves that are supplied with fuel from the fuel pump. The fuel is then squirted through a tiny nozzle, which atomizes the gas so it burns easier.

In the U.S., automakers discontinued the use of carburetors by the mid 1990s in exchange for the electronic system, which has better control over the fuel usage, so the ratio of gas-to-air is more accurate. This can both reduce emissions and improve fuel efficiency, but many motorists still swear by the mechanical carburetor because it can generate more horsepower than an electronic fuel injection system. This is also one of the reason carburetors are still used in racecars.