FAA Ground School Practice Test

What is the operating principle of float-type carburetors based on?

1. Difference in fuel type and temperature

2. Difference in air pressure at the venturi throat and the air inlet

3. Difference in engine RPM and fuel flow

4. Difference in altitude and atmospheric pressure

The correct answer is: Difference in air pressure at the venturi throat and the air inlet

The operating principle of float-type carburetors is based on the difference in air pressure at the venturi throat and the air inlet. In a float-type carburetor, fuel is drawn into the airstream due to a pressure difference created by the airflow through the venturi. When air passes through the venturi, its velocity increases and, according to Bernoulli's principle, the pressure decreases. The lower pressure at the venturi throat compared to the inlet allows atmospheric pressure to push fuel from the float chamber into the airstream, mixing fuel with air to create a combustible mixture for the engine. This principle is crucial for the carburetor's functionality, as it directly influences the airflow and fuel delivery characteristics that enable the engine to maintain the appropriate mixture for efficient combustion. The design of the float mechanism helps regulate fuel levels, ensuring consistent fuel delivery as demand varies during different engine operations. This understanding is essential for pilots and mechanics when troubleshooting fuel delivery issues or optimizing engine performance. The other answer choices do not pertain to the fundamental working principle of float-type carburetors, as they involve factors not directly related to the pressure and flow dynamics critical for fuel and air mixing within the carburetor.