With number 1 plug black soot and number 7 white it will definitely cause a stumble. Number 1 (dry soot correct? not greasy at all?) sounds like a cylinder not lighting off completely and number 7 being white is the scary one with possible water entering cylinder or lack of fuel. If soot is greasy then you know the answer. I would start with the basics, check firing order then pull valve covers and distributor cap. Roll engine over watching valvetrain is moving correctly with firing order. If good, for #1 black soot, check for a weak spark. cap, rotor, wires, gap on plug, ect. Something is killing the spark, water or oil normally wont leave it a dry black soot. Hard to believe its getting more fuel then the other 3 cylinders assuming it is a dual plane intake if carb was way out of adjustment (balance). #7 white, water or lack of fuel? Ya, duel plane thing again. No white exhaust smoke? wipe finger in tailpipe? Still good? Bring piston to the top and use paper towel to check for possible water. if sure all is dry remove carb and check for obstruction (shop towel?) it's been done before. Would also be a good time to re-torque head and intake bolts also. Dual plane intake is cyl: 1,4,6 and 7 off one side of carb 2,3,5 and 8 on the other so thats why I dont think carb, one black one white on same side of intake?. Just what i would do before digging deep.