Yeah, I agree with Robert - In order to run that rich either (1) the jets are really screwed up (highly doubtful) or (2) the fuel pressure is too high (very possible) and pushing too much fuel past the float valves. Neither of these can be fixed by playing with the mixture screws. A third possibility is some crud keeping the float valves open but that should probably only affect one side of the engine at a time - if all your plugs are satin black then revert to idea (2.)
Also, as Robert mentioned, it is important that we know the type of fuel pump (electric or mechanical) and the type of carburetor (make and model) as different carbs require different fuel pressures and yours sounds like the pressure is too high.
If you don’t know what or where to look for that info, just ask and we’ll guide you.