What are the three functions of the Venturi?

• A. Heats air before entering the intake
• B. Increases pressure at the discharge nozzle
• C. Limits airflow at idle only
• D. Proportions air-fuel mixture, decreases pressure at the discharge nozzle, and limits airflow at full throttle

Answer: (D)

The Venturi works by creating a high-velocity, low-pressure region in the intake as air is forced through a narrowed passage. That pressure drop is what pulls fuel from the discharge nozzle into the airstream, so the amount of fuel drawn is naturally tied to the amount of air flowing through the Venturi. In this way, the air and fuel are proportioned to produce the correct mixture.

The fixed throat also acts as a limiter on how much air can pass through. Even with the throttle opened fully, the Venturi’s geometry sets a maximum airflow, helping maintain a predictable, stable ratio across different operating conditions.

Heating the air before entry isn’t a function of the Venturi; it doesn’t increase pressure at the discharge nozzle (it actually corresponds to a pressure drop), and it isn’t solely about limiting airflow only at idle.