How does a carbeurated engine work?

Answer 1

Air drawn into the engine by the downward motion of the piston causes a vacuum as the air passes through the carburetor's venturi.

There are mainly 2 circuits:

The (idle circuit) delivers the fuel when the throttle is closed/mostly closed.

The (main circuit) delivers the fuel when off idle/normal driving.

The jets size controls how much fuel is sucked into the motor (controlling the air/fuel ratio, Ideally at 14.3:1).

There is a choke on most (street) carburetors that block air flow through the venturi causing the air/fuel ratio richen up, making cold starts easier.

There is a (power circuit) that allows a richer air/fuel ratio at wide open throttle, usually operated when the vacuum drops. Some carburetors use a stepped metering rod to control this function. A slightly richer air/fuel ratio( approx 12:1) creates more power.

An accelerator pump is used to force fuel through the jet when the throttles are quickly opened to prevent a lean condition (which normally causes the engine to stumble).

The main reason carburetors were replaced by fuel injection is that the transition between idle/main/power/accel pump is slower and not as accurate as EFI, causing emission to be higher and fuel economy to be lower.