What causes valve sticking in small motors?

Valve sticking in small motors typically occurs due to the buildup of fuel lead, gum, or varnish. These substances can accumulate over time from the combustion process, particularly if the fuel isn't of high quality or if there are issues with the combustion chamber. When these residues form, they can cause the valves to adhere to their seats or become obstructed in their movement, preventing them from operating smoothly.

Proper maintenance, including using good quality fuel and routine cleaning of the engine components, can help mitigate this issue. It’s important to understand that while excess lubrication and lack of fuel can cause other problems in a small motor, they are not responsible for valve sticking. Similarly, a faulty ignition system can lead to performance issues but does not directly cause the valves to stick.