The 1 barrel 1945 Holley on my Slant six is set on the rich side,plugs are carbon fouled.Which way do I turn the adjustment screw to lean it out?

screw them in. But that only affects idle.

does it smoke black while driving?

If you need to lean it overall, take it apart and check the float setting. you may need to lower the float level so there is less fuel in the bowl, creating less of a column of fluid, and therefore leaning out the fuel mixture.

Not sure exactly how to do it on that carb, but changing the jets and air bleed sizes will lean the carb out.

I would suspect if it is a used and dirty carb the air bleeds are clogged and it is "sucking" in too much fuel. They will be small (less then 0.01") holes which can been seen in the throat of the carb (at least on 4bbl holleys).

start there or do a complete rebuild.

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does it smoke black while driving

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Doesnt seem like it does(I dont see it) but it smells something awful if its idleing,as It was the other day while I was chit chatting with a friend.

Then yeah, screwing in the mixture screw should lean it out.

But, the seat could be damaged, or the needle could be damaged.
While running, screw it all the way in. You should be able to do it with your fingers, do not tighten.
It should kill the car.
If it does not, then shut off the car and pull it all the way out and see if it is still cone shaped. If there is a flat spot or whatever, someone cranked down on it and you are not metering fuel properly.

choke/choke pulloff