FAA Powerplant Written Practice Test

What is the likely outcome of an induction system leak near a cylinder?

1. A richer mixture

2. A lean mixture

3. Higher engine RPM

4. Lower fuel consumption

The correct answer is: A lean mixture

An induction system leak near a cylinder allows unmetered air to enter the engine, bypassing the carburetor. This results in an increase in the air-to-fuel ratio, which means there is more air relative to the amount of fuel being introduced into the combustion chamber. Consequently, this creates a lean mixture, where the fuel is not sufficient to properly combust with the added air. A lean mixture can lead to several performance issues such as rough engine operation, overheating, and potential engine damage if not corrected, as the ideal combustion process relies on a balanced mixture of fuel and air. Understanding how induction leaks affect the mixture is crucial for diagnosing engine performance issues and maintaining proper engine operation.