[Mgs] spark plug 2 and 3 has black sooth

[1971mgb at cox.net]

ok folks I'm still messing around with my HS4 carbs., I've adjusted the carbs to where I'm almost contend with the mixture, however my issue is that not all my spark plugs have that nice grayish color to them, if I'm looking at number 1 spark plug (nearest the radiator) and count toward the rear of the engine then number 4 would be near the heater box, having said that number one spark plug then is a nice gray and number 4 near the heater box is nice and gray that leaves number 2 and number 3 having black sooth on the them (bottom of spark plug). Do I need to lean out the carb nearest the front (near radiator) or the rear carb. nearsest the heater box?

Thank you all for your input.