What problem may occur if fuel vaporizes too readily?

When fuel vaporizes too readily, a condition known as vapor lock can occur in the fuel system. Vapor lock happens when the fuel transitions from a liquid to a vapor state before it is delivered to the engine, obstructing the flow of fuel. This can lead to a loss of fuel pressure, causing the engine to stall or run poorly due to insufficient fuel reaching the combustion chamber.

The other options, while related to potential issues with fuel or engine operation, do not directly address the specific consequence of excessive fuel vaporization. Contamination involves the introduction of impurities into the fuel system, poor engine performance can be a consequence of various issues besides vaporization, and losing altitude is a result of a loss of engine power rather than a direct result of fuel vaporization. Therefore, vapor lock is the most accurate answer in the context of readily vaporizing fuel.