Why is vapor lock serious?

• A. It can completely block fuel flow
• B. It reduces exhaust noise
• C. It increases engine speed
• D. It lowers fuel density

Answer: (D)

Vapor lock is serious because hot fuel in the lines and carburetor can vaporize, creating pockets of gas that disrupt the steady flow of liquid fuel to the engine. When fuel vaporizes, the liquid portion density in the delivery path drops, so less fuel mass reaches the combustion chamber for each intake cycle. That reduction in liquid fuel delivery leads to fuel starvation, power loss, or engine stalling. It isn’t about making exhaust quieter or speeding up the engine; it’s about the liquid fuel being replaced by vapor, which lowers the effective fuel density in the line and starves the engine of fuel.