FAA Powerplant Written Practice Test

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

1. A lean mixture.

2. A rich mixture.

3. No change in mixture.

4. Increased fuel consumption.

The correct answer is: A lean mixture.

An induction system leak near a cylinder introduces extra air into the intake system. This additional air dilutes the fuel-to-air ratio, resulting in a lean mixture. A lean mixture occurs when there is more air relative to fuel, which can lead to reduced engine power output and higher operating temperatures. This is due to the fact that combustion becomes less efficient when there isn't enough fuel to effectively utilize the added air. In contrast, a rich mixture would result from either too much fuel or a situation where less air is available than required for the amount of fuel being delivered. The terms related to "no change" or "increased fuel consumption" do not apply here since a leak will inherently alter the mixture and can also affect overall efficiency, potentially leading to increased fuel consumption, but the immediate result of the leak is the transition to a leaner mixture.