What is a symptom of a leaking exhaust valve during engine operation?

A symptom of a leaking exhaust valve during engine operation is often difficulty starting the engine. When an exhaust valve fails to seal properly, it can lead to a loss of compression in the affected cylinder. This loss of compression means that the air-fuel mixture doesn't ignite effectively, which can result in difficulty when trying to start the engine. Furthermore, the leakage may cause backpressure in the exhaust system, which can exacerbate starting problems.

In contrast, higher fuel efficiency, an increase in horsepower, and smoother idle performance are not typically associated with a leaking exhaust valve. A leaking valve generally disrupts the engine's performance, leading to reduced fuel efficiency and potentially causing a rough or unstable idle due to the improper mixture of air and fuel in the combustion chamber. This context provides a clearer understanding of how a leaking exhaust valve negatively impacts engine operation.