Which carburetor circuit is primarily responsible for metering fuel using jets and the main venturi to feed the discharge nozzle?

• A. Idle circuit
• B. Main metering circuit
• C. Float circuit
• D. Power circuit

Answer: (B)

The main metering circuit is the part that controls fuel flow during normal engine operation, using the main jets and the main venturi to meter fuel to the discharge nozzle. As air passes through the main venturi, a pressure drop draws fuel from the float bowl through the main jets, and this fuel is delivered to the discharge nozzle where it mixes with the incoming air. This arrangement sets the air-fuel ratio across mid to high throttle ranges. Other circuits serve different roles—idle circuit handles fuel at very low speeds with its own idle jet, the float bowl stores and supplies fuel to these circuits, and the accelerator pump (power circuit) provides a brief extra fuel shot during sudden throttle openings—but the main metering circuit is the one responsible for metering fuel via jets and the main venturi to feed the discharge nozzle.