What does black, sooty carbon on all four spark plugs indicate? I pulled all four plugs and all are pretty sooty. Too rich, too lean, too advanced/retarded spark?
I'll say too rich.
Too rich. Try tuning in (clockwise) on the cab adjuster unit the engine starts to sputter, then out just a touch. Also make sure that the float in the carb is set to the proper level.
I agree with Mark and Rod. Once you've made the adjustment watch for overheating in case you may have leaned it out a little too much.
Too rich or too cold a plug!
Definitely too rich. Experience talkin' here. Did this on my '27 Tudor to the point where the car wouldn't start! I got smarter though.
How about worn rings and burning a little oil? But I would try adjusting the carb first.