What is a common issue indicated by low compression in a four-stroke engine?

Low compression in a four-stroke engine often indicates issues with the engine's valve assembly. Over time, valves can become worn, misadjusted, or damaged due to various factors such as overheating, lack of lubrication, or poor maintenance, leading to improper seating. When the valves do not fully close, they allow air-fuel mixture to escape, resulting in lower compression readings during a compression test. This is crucial for the engine's overall performance because proper compression is necessary for effective combustion and power generation.

In contrast, while ignition faults, fuel contamination, and excessive oil consumption could affect engine performance, they do not directly relate to low compression measurements. Ignition problems would typically manifest as misfires or stalling rather than affecting the compression of the engine's cylinders. Fuel contamination might lead to poor combustion or running issues, but again, it would not impact the compression itself. Excessive oil consumption often signals issues with piston rings or cylinder walls rather than with the valve system. Therefore, faulty valves are the most relevant issue concerning low compression in a four-stroke engine.