In terms of fuel delivery, which occurrence is least likely to cause vapor lock?

Direct fuel injection is least likely to cause vapor lock because of the way this system operates. In direct fuel injection, fuel is injected directly into the combustion chamber at high pressure, which helps keep the fuel in a liquid state even under varied temperature conditions. This high-pressure environment minimizes the likelihood of vapor formation that can lead to vapor lock, allowing the fuel to bypass conditions that might typically lead to vaporization.

In contrast, situations such as carburetor flooding, excessive heat in the fuel lines, and inadequate fuel pressure are more likely to promote vapor lock. Carburetor flooding can lead to excess fuel in the carburetor bowl, where higher temperatures can cause the fuel to vaporize and create a bubble in the fuel system. Excessive heat in fuel lines, especially in areas close to the engine, can also lead to vaporization of fuel, contributing to vapor lock. Inadequate fuel pressure may result in insufficient fuel reaching the engine, which can cause the fuel to vaporize and impede fuel delivery. These factors create conditions that are more favorable for vapor lock compared to the direct injection method.