What is the difference between a carburetor-based induction system and a port/fuel-injection system in terms of metering?

What is the difference between a carburetor-based induction system and a port/fuel-injection system in terms of metering?

• A. Carburetor meters fuel electronically, while EFI meters fuel by air flow.
• B. Carburetor meters by air flow; EFI meters fuel based on sensors.
• C. Carburetor meters fuel by air flow via venturi and choke; EFI meters fuel electronically based on sensors and engine operating conditions.
• D. Carburetor and EFI both meter fuel identically.

Answer: (C)

Fuel metering is handled in two very different ways. In a carburetor, the amount of fuel entering the engine is controlled by the airflow itself. As air is drawn through the throttle bore and a venturi, its speed increases and pressure drops, which pulls fuel from jets into the airstream. The mixture is determined by the carburetor’s fixed geometry and components like the venturi size, choke, jets, and floats, so fuel flow roughly tracks air flow but is not actively measured or adjusted by sensors. In a port/fuel-injection system, metering is electronic. The engine control unit uses sensors to determine air mass, speed, load, temperature, and other conditions, then computes the exact fuel amount and times the injectors to deliver it at the right moment. This electronic control, often with closed-loop feedback from an oxygen sensor, allows precise, real-time adjustments across a wide range of conditions, and fuel is injected into the intake ports rather than being drawn in passively by air flow alone. That combination of airflow-driven metering in a carburetor versus sensor-based, electronically controlled metering in EFI is why the two systems differ so fundamentally in how they determine fuel quantity.

Fuel metering is handled in two very different ways. In a carburetor, the amount of fuel entering the engine is controlled by the airflow itself. As air is drawn through the throttle bore and a venturi, its speed increases and pressure drops, which pulls fuel from jets into the airstream. The mixture is determined by the carburetor’s fixed geometry and components like the venturi size, choke, jets, and floats, so fuel flow roughly tracks air flow but is not actively measured or adjusted by sensors.

In a port/fuel-injection system, metering is electronic. The engine control unit uses sensors to determine air mass, speed, load, temperature, and other conditions, then computes the exact fuel amount and times the injectors to deliver it at the right moment. This electronic control, often with closed-loop feedback from an oxygen sensor, allows precise, real-time adjustments across a wide range of conditions, and fuel is injected into the intake ports rather than being drawn in passively by air flow alone.

That combination of airflow-driven metering in a carburetor versus sensor-based, electronically controlled metering in EFI is why the two systems differ so fundamentally in how they determine fuel quantity.