Vapour Lock

Vapour lock:
When the fuel line is mounted in a warm place, e.g. right alongside a hot part of the engine, vapour lock can occur in the line. This means that, due to the heat of the line, a petrol vapour bubble can form. This will partially or completely interrupt the fuel supply.
To prevent this, the fuel line must always be mounted at some distance from hot engine parts and be insulated as well as possible. Keeping sufficient pressure in the system also prevents this. In a liquid system that is under pressure, the liquid will not start to boil at 100 degrees Celsius. Think of the cooling system in a car: the coolant can also reach 120 degrees when it is under pressure without boiling. The coolant will only start to boil when the pressure is released from the system.