What is a common result of an excessively rich mixture in an aircraft engine?

An excessively rich mixture in an aircraft engine can lead to engine roughness due to a few key factors. When the fuel-air mixture contains too much fuel relative to the amount of air, it can cause incomplete combustion. This incomplete combustion leads to unstable engine operation and can produce irregular power delivery, resulting in rough running. The excess fuel can overwhelm the combustion process, creating a situation where not all the fuel is burned efficiently.

In contrast, an excessively rich mixture does not enhance fuel efficiency, as more fuel is being burned without corresponding power gains. Rather, it can lead to wasted fuel and increased emissions. Similarly, while an increase in power might be temporarily experienced when the mixture is rich, it often results in lower performance over time due to the adverse effects of carbon buildup and fouling of spark plugs. Therefore, the result of rough engine operation is a significant indicator of an excessively rich mixture in the context of engine performance.