I have with the help of our local Rolls Royce guru come up with another theory regarding this problem, follow along with me as I may ramble on.
The fuel pump in my particular rolls is the later type, I am theorizing that this pump runs constantly therefore it has a return line to complete the circuit or else the pump would just send too much pressure and fuel to the carbs, if this is in fact the case then on the return line there would be a check valve of sorts to keep the fuel flow going in the proper direction and not gravity feeding on the return side from the tank. If this check valve is not opening or gets stuck or is gummed up, whatever, then the return flow of fuel would be stopped causing the pump to over load the carb or carbs therefore forcing an overflow situation as the fuel that would normally go through in the return line to essentially stop.
So when I shut the engine down and the pump stops the pressure is stopped, the check valve if it exists gets un-stuck and when I restart the engine all is well with the flow and no more leak.
That's my latest theory, now if there is no return on the pump then it's just plain old stuck needle valves, I am wanting to doubt that because the carbs including floats were rebuilt. Anything is possible. And with this Ethanol excuse for gasoline anything is possible, **** corn squeezin's!!!