How can improper valve clearance affect engine performance?

Improper valve clearance primarily affects engine performance by leading to poor engine compression and causing misfire issues. When the valve clearance is not set correctly, it can result in valves either opening too late or closing too early, which can significantly impact the timing of the combustion process. If the intake valves do not open fully or close at the right moment, the engine may not be able to draw in enough air-fuel mixture or may result in incomplete combustion. This ultimately reduces the engine's compression, making it difficult for the engine to maintain efficient operation and leading to misfires, where the engine fails to fire consistently on each cycle. This situation can cause poor acceleration, reduced power output, and increased emissions, affecting overall performance and drivability.