FAA Powerplant Written Practice Test

What ensures fuel supply in the idling range for an engine equipped with a pressure-type carburetor?

1. A special fuel filter

2. A spring in the unmetered fuel chamber

3. An automatic shut-off valve

4. Additional fuel injectors

The correct answer is: A spring in the unmetered fuel chamber

The correct answer emphasizes the role of a spring in the unmetered fuel chamber of a pressure-type carburetor, which is crucial for ensuring an adequate fuel supply during idling. In a pressure-type carburetor, fuel is metered based on the differential pressure created by the airflow in the venturi. The spring in the unmetered fuel chamber maintains a specific pressure that regulates the flow of fuel into the carburetor, ensuring that there is always a sufficient supply of fuel even when the engine is idling, where lower airflow could otherwise hinder fuel delivery. This mechanism is essential because during idling, the engine operates at low RPMs and can have variable demands for fuel. The spring helps to stabilize the fuel delivery by adjusting the pressure to ensure that fuel can flow into the system as needed, preventing stalling or rough idling conditions. The other options relate to different components or systems that, while significant for overall engine operation and safety, do not directly address the idling fuel supply function in a pressure-type carburetor.