FAA Powerplant Written Practice Test

What occurs when the vapor vent float in a pressure injection carburetor loses its buoyancy?

1. The fuel supply to the engine will decrease

2. The fuel returning to the tank will be increased

3. The engine will experience a lean mixture

4. The carburetor will flood with fuel

The correct answer is: The fuel returning to the tank will be increased

When the vapor vent float in a pressure injection carburetor loses its buoyancy, it becomes unable to effectively regulate the vapor venting process. In this situation, the loss of buoyancy typically leads to increased fuel pressure in the system. As a result, more fuel is returned to the tank because the float is no longer able to maintain the proper level to allow for optimal vapor venting. This excess fuel can be directed back to the fuel tank instead of being delivered to the engine, which corresponds to an increase in the returning fuel. Understanding this system is crucial, as the proper function of the vapor vent float directly affects the carburetor's ability to manage fuel delivery and ensure efficiency in engine performance. The interaction between buoyancy and fuel management is a key principle in carburetor operation, especially in pressure injection systems.