What is a common operational issue that can result from improper fuel mixture?

Improper fuel mixture can lead to decreased engine power due to the incorrect balance of fuel and air that is introduced into the combustion chamber. An overly rich mixture, which has too much fuel and not enough air, can cause incomplete combustion. This results in lower power output because the engine is unable to operate efficiently; some of the fuel does not burn completely, leading to wasted energy and reduced performance. Conversely, a mixture that is too lean, with too much air and not enough fuel, can also reduce engine power as it can lead to insufficient energy release during combustion. Both scenarios negatively affect the engine's ability to generate the required thrust for proper operation.

Increased flight speed, improved fuel economy, and enhanced smooth running are generally desirable outcomes that can occur from an optimal fuel mixture, but when the mixture is improper, they are unlikely to be realized. Hence, the choice related to decreased engine power is the one that accurately reflects a common operational issue associated with improper fuel mixtures.