Which of the following is a symptom of stale gasoline?

Frequent engine stalling is indeed a symptom of stale gasoline. Over time, gasoline can degrade and lose its effectiveness, particularly due to factors like evaporation or the absorption of moisture. When gasoline becomes stale, it may not combust properly, leading to inconsistent fuel delivery to the engine. As a result, this can cause the engine to stall frequently, as it struggles to maintain operation with subpar fuel quality.

Stale gasoline also tends to lead to various performance issues such as poor acceleration and rough idling due to its altered chemical composition. Regularly using fresh gasoline is essential to ensure optimal engine performance and reliability. Conversely, increased horsepower, clear exhaust smoke, and improved ignition are not associated with stale gasoline, but rather indicate good fuel quality performance.