With a carburetor engine there is usually a fuel pump on the side of the block, operated by the camshaft. Vapour lock nearly always originates in the last foot of fuel line before the pump, because the fuel is being sucked up-hill in that section. Being subjected to less than atmospheric pressure makes the fuel especially likely to generate vapour. However under slightly more severe conditions you will get vapour lock even if you have an electric pump in the top of the fuel tank, as the last of the carburetor cars often did. By the way, in the good old days we used to be able to get home despite vapour lock by wrapping a wet rag around that last bit of fuel line before the pump: the evaporation of the water cooled it enough to get us going for a while, until the rag dried and we had to soak it in water again.
In the days of the carburetor engines, car manufacturers used to fit 'vapour return lines' when necessary, to remove petrol vapor from the fuel line just before the carburetor. If you want to see how this works look at any carburetor-engine Commodore or full-sized Holden and compare the air-conditioned model (which always had a vapour return system) with the non-air-conditioned model (which didn't, because it had lower under-hood temperatures). Nowadays, fuel injected cars nearly always have a recirculating fuel system, with a swirl pot in the top of the fuel tank to separate the vapour from the returned fuel, so vapour lock has almost disappeared as a problem. My own car happens to be the only port-fuel-injected design I have ever encountered that does not have either recirculating fuel, or a vapour return line, so it suffers from vapour lock in summer.
You could remove the vapour lock from your Datsun by bleeding the fuel line at the carburetor intake fitting, like bleeding a diesel fuel line, or a brake system. However to keep it from happening again in a few seconds, you might need to do the wet rag trick.
