What might cause a rich fuel mixture in an engine?

A rich fuel mixture in an engine occurs when there is an excess of fuel relative to the amount of air in the combustion chamber. This can be caused by an excess fuel flow into the combustion chamber. When more fuel is introduced than the engine is designed to utilize, the air-fuel ratio becomes unbalanced, resulting in a rich mixture.

This rich mixture can be influenced by factors such as a malfunctioning fuel pump, a stuck injector, or incorrect adjustments in the fuel delivery system. In such cases, the engine may struggle to achieve optimal combustion efficiency, leading to issues such as increased emissions, rough running, or fouled spark plugs.

Other options, like insufficient fuel supply and excess air entering the combustion chamber, would lead to a lean mixture rather than a rich one. Normal engine operation would indicate that the fuel and air are properly balanced under standard conditions. Understanding these dynamics is crucial for diagnosing engine performance and ensuring efficient operation.