Check the top carburetor casting for warp. Rochester Bs are notorious for getting a bowed-up top casting that causes a vacuum leak. This forces the mixture to go full rich by holding the power valve open constantly and there's nothing you can do to adjust it away. You could also have set the float level slightly too high which will cause the carburetor to flood at idle and soot up the plugs.

The fix ix simple- - - -Use the Rochester for a paperweight ( a stinky one because it's had gasoline in it) and install a Carter carburetor. Like Carter's advertising slogan in the 1950s said- - - - -"The ABCs of carburetion are Always Buy Carter!"
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!