From 1976 Pontiac Service Manual:
"A new design fuel filter with integral check valve to meet Federal safety regulations for fuel loss during vehicle roll-over."
This would stop fuel draining from fuel tank to the ground thru the carb at roll-over, not so much draining carb TO the fuel tank.
Since it acts like a restriction on fuel flow i would not use it for a pre-1975 engine or any high performance engine.
