Carburetor loses prime after 8+ hours

ive had a few carburetors percolate before, usually when its hot out, when id shut down my big block i could pop off the air cleaner and see the fuel evaporating out of the vent stacks. a thicker base gasket instead of a thin crappy paper one and the problem disappeared all together. Ive also seen fuel pumps leak into the crankcase or vent hole on the side of the pump body as well, losing prime. so if its "making its own oil" thats a pretty good indicator. if all else fails try a fuel pump check valve, napa used to sell em but discontinued them for some stupid reason. im sure theyre available from other vendors.