Hi,
you should also check that you have the breather in the fuel tank exists and is not blocked. What can happen is you drive it around fine all day but the fuel tank is pressurising because it can't get fresh air and then overnight it draws the fuel back from the carby, pump and filter.
Before you try to start it in the morning, inspect the float bowl(as per Steam) and the filter and see if they have fuel in them. It is sounding like you have to pump fuel up from an empty pump and filter.
Terry