Definitions for vapor lock
Random House Webster's College Dictionary
an obstruction to the flow of fuel to a gasoline engine caused by the formation of bubbles in the fuel.
Category: Automotive, Physics
vapor lock, vapour lock(noun)
a stoppage in a pipeline caused by gas bubbles (especially a stoppage that develops in hot weather in an internal-combustion engine when fuel in the gas line boils and forms bubbles that block the flow of gasoline to the carburetor)