<P> Vapour lock is a problem that mostly affects gasoline - fueled internal combustion engines . </P> <P> It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system . This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling . Restarting the engine from this state may be difficult . </P> <P> The fuel can vapourize due to being heated by the engine, by the local climate or due to a lower boiling point at high altitude . In regions where fuels with higher volatility are used during the winter to improve engine startup, continued use of the specialized fuels during the summer can cause vapour lock to occur more readily . </P> <P> Vapour lock was far more common in older gasoline fuel systems incorporating a low - pressure mechanical fuel pump driven by the engine, located in the engine compartment and feeding a carburetor . Such pumps were typically located higher than the fuel tank, were directly heated by the engine and fed fuel directly to the float bowl inside the carburetor . Fuel was drawn under negative pressure (gauge pressure) from the feed line, increasing the risk of a vapour lock developing between the tank and pump . A vapour lock being drawn into the fuel pump could disrupt the fuel pressure long enough for the float chamber in the carburetor to partially or completely drain, causing fuel starvation in the engine . Even temporary disruption of fuel supply into the float chamber is not ideal; most carburetors are designed to run at a fixed level of fuel in the float bowl and reducing the level will reduce the fuel to air mixture delivered to the engine . </P>

What causes a car engine to vapor lock
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