Vapor Lock

[Alaskan]

Vapor lock occurs when the vapor pressure of the fuel is higher than the surrounding environment. In older engines with "sucking" fuel pumps at the engine the pressure in the fuel line to the tank is reduced by the sucking action of the fuel pump drawing fuel form the fuel tank, and when heated, the gasoline actually boils creating a vapor of gasoline which the fuel pump can not handle, thus the name "vapor lock".
More than likely if it did vapor lock it was becasue of the headers or exhaust pipes. If it keeps happening try rapping the pipes.