In all internal combustion engines, the carbureted engines is the component that supplies fuel to the engine. Even on other equipment, like lawnmowers and chainsaws, it serves the same purpose. As cars have evolved, the carburetor become more complex in order to handle all of the operating requirements. For instance, to handle some of these tasks, carburetors had five different circuits:
- Main circuit – Provides the right amount of fuel for cruising
- Idle circuit – Sends just enough fuel to keep the engine idling
- Accelerator pump – An extra burst of fuel at acceleration, which reduces the hesitation before the engine speeds up
- Power enrichment circuit – When going up a hill or towing, this provides a boost of fuel.
- Choke – Gives extra fuel when the engine is cold so it’ll start
In order to meet stricter emissions, catalytic converters were invented, but very careful control of the air-to-fuel ratio was needed for “cats” to be effective. Oxygen sensors watch the amount of oxygen in the exhaust, and then engine control unit (ECU) uses this info to adjust the ratio immediately. This is called closed loop control — it was not feasible to achieve this control with carburetors.
At first, carbureted engines were replaced by throttle body fuel injection systems (also called single point or central fuel injection systems), which had electrically controlled fuel-injector valves into the throttle body. These could be swapped directly with a carburetor, so automakers didn’t have to make any big changes to their engine designs.
As new engines came along and continued to change, the throttle body fuel injection was replaced by multi-port fuel injection (or port, multi-point or sequential fuel injection). These have a fuel injector for each cylinder and they’re typically located so they spray right at the intake valve. These systems provide more accurate fuel metering and faster response.
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