FAA Powerplant Written Practice Test

On an engine equipped with a pressure-type carburetor, how is fuel supply in the idling range maintained?

1. Through manual control

2. By a spring in the unmetered fuel chamber

3. Using electronic sensors

4. By atmospheric pressure adjustment

The correct answer is: By a spring in the unmetered fuel chamber

The maintenance of fuel supply in the idling range of an engine equipped with a pressure-type carburetor is primarily achieved by a spring located in the unmetered fuel chamber. In a pressure-type carburetor, the fuel is delivered based on the differences in pressure and is regulated to ensure that the engine receives the appropriate mixture, even at low engine speeds. When the engine is idling, the airflow is minimal, creating a lower pressure that could affect the fuel flow. The spring in the unmetered fuel chamber plays a crucial role by exerting pressure that helps to maintain an adequate supply of fuel. This ensures that the fuel is delivered efficiently to the engine under varying conditions of throttle position and airflow, thus enabling smooth operation and stable idling. While manual control, electronic sensors, and atmospheric pressure adjustments can play roles in different types of fuel delivery systems, they are not the primary mechanisms for maintaining fuel supply in the idling range of a pressure-type carburetor. The spring's action in the fuel chamber is what directly influences fuel flow during idle conditions, ensuring that the carburetor remains responsive and effective.