What is one consequence of allowing an engine's timing to remain off over time?

Allowing an engine's timing to remain off over time can lead to increased emissions. The engine timing, which refers to the precise moment when the spark plug ignites the air-fuel mixture in the combustion chamber, is crucial for optimal engine performance. When the timing is not set correctly, the combustion process can become inefficient.

This inefficiency means that not all of the air-fuel mixture is burned completely or optimally, leading to incomplete combustion. As a result, unburned hydrocarbons and other pollutants may be emitted from the exhaust system, contributing to an increase in harmful emissions. Additionally, poor timing can lead to a rise in engine temperature and pressure, further exacerbating the emissions problem.

In contrast, options such as improved fuel economy, smoother performance, and higher horsepower are reliant on precise timing for maximizing engine performance, so they are unlikely to be a consequence of having incorrect timing over an extended period. Instead, proper timing typically enhances these attributes, whereas neglecting timing adjustments tends to have the opposite effect.