Gently seat/shut the idle mixture screw (close, turn in, righty tightly). If the motor runs with the idle mixture screws shut it is getting fuel from somewhere else other than the idle circuit. This would lead to a possible power valve bad or mismatched to motor vacuum. It is also a sign of a possible vacuum leak.

However, vacuum leaks usually run lean. With your motor running rich, I would suspect high fuel pressure, high float setting or a mismatched power valve.

Fuel pressure needs to be confirmed first (or at least do what another suggested and disconnect the fuel and see if it runs on the float bolt's fuel only OK), otherwise you're chasing your tail.
Second would be to check the power valve to see what rating is marked on it, and change it to a higher vacuum rating..