Which symptom may indicate a marine engine is misfiring?

A symptom indicating that a marine engine is misfiring is rough idling during operation. When an engine misfires, it usually means that one or more cylinders are not firing correctly, leading to irregular combustion. This results in the engine running unevenly, which manifests as a rough or unsteady idle.

In contrast, consistent engine performance and smooth acceleration are signs of a well-functioning engine, indicating that all cylinders are firing properly, and the engine is operating efficiently. Increased fuel efficiency typically suggests that the engine is operating optimally, maintaining good combustion and fuel use, which would not be the case if it were misfiring.