FAA Powerplant Written Practice Test

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

1. Before the Venturi

2. Between the Venturi and the engine

3. At the fuel inlet

4. After the engine

The correct answer is: Between the Venturi and the engine

The throttle valve in a float-type carburetor is positioned between the Venturi and the engine. This positioning is crucial for controlling the amount of air-fuel mixture that enters the engine. When the throttle valve opens, it allows more air and fuel to flow into the engine's intake manifold, increasing power and engine speed. Conversely, when the throttle valve is closed, it restricts the flow of air and fuel, reducing power and engine speed. In this context, the Venturi is the section of the carburetor that creates a low-pressure area, allowing fuel to be drawn into the airstream from the float chamber. Positioning the throttle valve after the Venturi ensures that the air-fuel mixture has already been atomized before it reaches the engine, optimizing combustion efficiency. Understanding this arrangement is essential for troubleshooting and maintaining engine performance, as any issues with the throttle valve position or function can directly impact engine operation and response.