It sure would be helpful if you'd specify which BS38's you have. In all of them, the upper hose barbs open into the tops of the float chambers. They must be open to atmosphere. If fuel is pouring out of them it means your float valves aren't shutting off fuel flow.
I assume that the lower barbs you're referring to aren't for the fuel line crossover, as that would be pretty obvious. If you're referring to the barbs on the float bowls, those are connected to the brass float chamber vent pipes in the float bowls. When fuel level passes the level of the pipe fuel overflows the pipe and comes out the barb. That only happens if the float system isn't controlling fuel; the primary function of the vents is to relieve vacuum caused by lowering of the fuel level in running. Again, those lines should be open to atmosphere, not linked. If the lower barbs are on the carb bodies then you're looking at an early carb set with a single enricher ("choke") valve, and the line carries enriched fuel mixture to the carb without a valve.
BTW when I say a barb must be open to atmosphere, that means that you put an open line on it; if you don't use a line crud can get sucked in by the weak vacuum developed as fuel depletes.
