I once owned when i was in college a 1974 Volkswagen Super Beetle. I loved that car, but I had to get rid of it due to a couple of problems. One of the problems we solved easily, but the other is one that still boggles me to this day. Upon taking it on the highway and shifting into fourth, as soon as I would hit sixty MPH the engine would make a loud metallic clunk, almost like someone lifting the engine lid and slamming it down. The engine would then sputter and stall and would not restart for another hour or so or start spraying gasoline out of the carb. We replaced the carb three times, twice with used ones and once with a new one and went through countless rebuild kits. The problem persisted. Does anyone know what may have been the cause of this and what might have been going on?
The emissions were really taking hold on the 73 and 74 model Beetles, and making a wild guess here, my opinion would be that the car was experiencing a fuel tank venting problem. This would cause the car to reach a point where the fuel pump could not pull fuel from the tank or the tank was pressuring up; the latter could be the cause of the gasoline spraying out of the carb.
The later VW Rabbits made after the Beetle also suffered at times from a fuel tank vent problem. When this occurred engine vacuum would actually suck the gas tank near flat and total capacity would be about 3 gallons at the most.
Many were towed in after someone filled their car up and ran out of gas shortly thereafter. The car owners could not understand why it would only take a few bucks to fill one up. 
It was easily determined by looking up underneath the car; the gas tank would barely even touch the straps that held it in the car. Kind of like placing a fingertip on the end of a soda straw and sucking the straw. The straw will crush just like the gas tanks.
One thing that was similar to this was a BMW motorycycle that I bought new back in the 70s (also under the emissions gun).
Right after buying the bike I started having trouble with the carburetors spraying gasoline, refusing to start, etc. and it was all traced back to a faulty vent in the gas cap. This led to a recall being issued; after I received gasoline in the face several times while unscrewing the tank cap.