Why must fuel lines have gentle slopes and no sharp curves?

• A. To prevent vapor lock
• B. To increase pressure
• C. To reduce weight
• D. To improve filtration

Answer: (A)

Fuel lines must keep liquid fuel in contact with the line and avoid trapping vapor. Vapor lock occurs when fuel vapor forms in the line and acts like an air barrier that the pump can’t push through, cutting off fuel delivery. Sharp curves and abrupt direction changes create pockets where vapor can collect and air can be drawn in, especially in hot engine areas. A gentle slope helps keep the line filled with liquid, lets any vapor migrate away from the pump, and reduces pressure drops that encourage boiling. With these features, the engine receives a steady flow of liquid fuel and is less prone to stalling from vapor lock.