FAA Powerplant Written Practice Test

What is the main function of an altitude mixture control in a carburetor?

1. Increases throttle response

2. Regulates the fuel/air mixture richness

3. Maintains engine temperature

4. Controls fuel pump pressure

The correct answer is: Regulates the fuel/air mixture richness

The main function of an altitude mixture control in a carburetor is to regulate the fuel/air mixture richness. As an aircraft ascends to higher altitudes, the air becomes less dense, leading to a lower amount of oxygen available for combustion. To maintain optimal engine performance and prevent the engine from running too rich due to the decreased air density, the altitude mixture control allows the pilot to adjust the fuel flow entering the carburetor. By leaning the mixture, pilots can ensure that the correct ratio of fuel to air is achieved, which is crucial for efficient combustion and engine performance at varying altitudes. This adjustment helps prevent issues such as engine roughness or fouling, which can occur if the mixture is too rich as altitude increases.