Vapor lock occurs when fuel vaporizes in the fuel lines, causing fuel starvation. Which induction system is most prone to vapor lock?

• A. Vapor lock is fuel vaporization in fuel lines, causing fuel starvation; carbureted systems are most prone, especially in high heat conditions, poor fuel quality, or long hot runs.
• B. Vapor lock refers to air leaks in the intake manifold.
• C. Vapor lock is caused by excessive fuel pressure.
• D. Vapor lock is a sensor fault causing misfire.

Answer: (A)

Vapor lock happens when the fuel in the lines turns into vapor and can’t flow as liquid to the engine, causing fuel starvation. The induction system most prone to this is carbureted engines. In a carbureted setup, fuel travels through lines and into the carburetor at relatively low pressure and sits closer to hot engine components. Heat can cause the fuel in those lines to vaporize, forming pockets of gas that the pump can’t push effectively, which starves the engine of liquid fuel and leads to stalling or hard starting after hot runs. Fuel-injected systems operate at higher pressures and manage fuel delivery differently, so they’re far less susceptible to vapor lock in typical conditions.

Other options describe issues that aren’t about liquid fuel starvation from vapor formation: air leaks in the intake cause misfiring or leaning, not vapor lock; excessive fuel pressure tends to cause flooding rather than vapor lock; and a sensor fault causing a misfire is unrelated to vaporized fuel lines.