FAA Powerplant Written Practice Test

Where is the throttle valve positioned in a float type carburetor?

1. Before the Venturi

2. After the engine

3. Between the Venturi and the engine

4. In the fuel tank

The correct answer is: Between the Venturi and the engine

In a float type carburetor, the throttle valve is positioned between the Venturi and the engine. This placement is essential for controlling the airflow into the engine, thereby regulating the engine's power output. The throttle valve's function is to adjust the amount of air/fuel mixture that enters the engine, and positioning it here allows for effective management of the engine's speed and power. When the throttle is opened, more air enters the Venturi, which also draws more fuel from the float chamber, creating a richer fuel mixture for combustion. Conversely, when the throttle is closed, the airflow decreases, which reduces the amount of fuel entering the engine. This precise control contributes to the overall performance and efficiency of the engine. In contrast, positioning the throttle valve before the Venturi would interfere with the airflow dynamics required for proper fuel atomization and could lead to poor engine performance. A location after the engine would not serve its purpose, as it would not regulate the intake of the air/fuel mixture into the combustion chamber. Positioning it in the fuel tank is impractical and irrelevant to the function of a carburetor.