Black soot ok plugs

Hey slant nation I got some concerns on my slant and wanted to see if u guys have any input or can lead me in the right direction. I have.' 66 170 with a Holley 1920 .its an original carb I have rebuilt it about 3 months ago and set the float to the best of my knowledge which is half way to the body of the carb. The kit never came with the gauge stick to do any accurate setting. It ran fine after that till about 3 or 4 days ago. It started idling low and leaving a black spot on my driveway from the tail pipe . It has never done this before ..I adjusted the carb to the best I can.I'm assuming it might be the carb again , making it run rich but I just checked my plugs and they look fine .theyre not white or black they're a light tan color. I also discovered a little black splurge on the surroundings of the intake runners in the manifold . Is that another sign of running rich? Or is it just some loose intake nuts that I have to tighten which I already snugged up a bit.ive been thinking of going super six but now I wanna wait and fix this problem before I do some light mods.i also have adjusted my valves to .11and .21 and I have the electronic ignition to mining is at about 10btc. Sorry for the essay but I need some fellow slant sixers help. Thanks in advance guys