Which of the following is NOT a factor related to vapor lock issues?

In the context of vapor lock issues, water contamination does not directly contribute to the occurrence of vapor lock. Vapor lock typically arises from the fuel vaporizing excessively due to high temperatures or low pressure in the fuel lines, which can lead to the formation of vapor bubbles that disrupt fuel flow to the engine.

Excessive heat is a primary factor because it increases the likelihood of fuel vaporizing within the fuel lines. Fuel vaporization directly relates to the problem since vapor lock is essentially caused by the fuel turning into vapor and blocking flow. Fuel line blockage can also create conditions that contribute to vapor lock by preventing liquid fuel from reaching the engine, thereby increasing the likelihood of vapor formation.

Water contamination affects fuel quality but does not cause vapor lock directly. While water can lead to engine performance issues or other complications, it does not contribute to the vapor lock phenomenon in the same way that the other choices do.