FAA Powerplant Written Practice Test

In what position should the carburetor heat be set when starting a piston-powered engine?

1. Hot

2. Cold

3. Warm

4. Variable

The correct answer is: Cold

When starting a piston-powered engine, the carburetor heat should be set to the 'Cold' position. In this position, the carburetor is supplied with outside air, which is generally cooler and helps prevent the buildup of ice that can occur in the carburetor if warm, humid air is used. Starting the engine with the carburetor in the cold position allows for optimal fuel-air mixture atomization, ensuring a smoother and more reliable engine start. Using the carburetor heat in the 'Hot' position during start-up directs warmer air into the carburetor, which may be necessary during actual flight conditions to prevent icing, but it can lead to poor start characteristics in cold weather. Setting it to 'Warm' does not provide the benefits of fully cold air either, as it may still allow some moisture to remain in the intake system. A 'Variable' position could introduce unnecessary complexity and variance, which is not standard practice during the start-up phase. Hence, the cold position is typically the recommended practice for starting to ensure the best performance of the engine.