With the mechanical fuel pump, there's no need for a fuel regulator, it's only pumping 3-5 psi anyway.
A few things to check, Evap connections and your fuel filter. Obviously the fuel is not sitting in the carb after long periods, meaning it's draining back or evaping.
1st the fuel filter and return line. The fuel filter must be the 1 line in, two out kind. pump.. -filter= carb and return line. The two out, must be on the carb side, not the pump side. Also, the carb line must be the lower one, return line on top, reason being, this bleeds off the exess pressure back to the tank. If you have em flipped, (carb feed on bottom) the fuel will slowly leak back into the tank overnight. Also the filter MUST be at least as high as the connection at the carb, if it's lower, the bowl will drain back. (Hence the ugly steel hard lines holding the fuel lines up over your calve cover)
Check the evap system, make sure all hoses are tight and connected. (underneath windhield washer resivior) if one is disconnected it'll slowly evap the fuel from the carb overnight disipating it into the air. You won't smell it because of the charcoal inthe canister.