In which scenario might an engine exhibit rough running?

An engine may exhibit rough running when the timing is off. Engine timing refers to the precise coordination between the engine components, particularly the timing of the spark plug firing and the position of the piston. If the timing is not set correctly, it can lead to several issues such as misfires, poor combustion, and ineffective power delivery, all of which contribute to rough engine operation.

In contrast, a proper fuel mixture, regular maintenance, and clean fuel injectors are all factors that help promote smooth engine performance. A proper fuel mixture ensures that the right amount of air and fuel is delivered to the engine, which is crucial for optimal combustion. Regular maintenance takes care of various engine components and systems to prevent wear and malfunction. Clean fuel injectors ensure that fuel is delivered effectively and evenly to the engine, preventing any issues related to fuel delivery.

Therefore, a misalignment in timing fundamentally disrupts the engine's operation, leading to rough running.