If it is flooding out the float could be set too high or there could be something holding the needle partially open to allow too much fuel into the bowl. When you look down the throat you should not see any fuel dripping. does it smell rich. If it is dripping fuel it should smell rich and the plugs should be black, which you say they are not so possibly scratch that idea.
On the other hand like Robert said you have the possibility of a vacume leak. OR have you adjusted the idle mixture screws or just adjusted the idle speed. Poor idle mixture can also give the symptoms you describe. A lot like slowly running out of fuel. We are all just guessing here without being able to see the problem.