Why is every OTHER plug sooty on my 401

[exchaoordo]

I've got soot on every OTHER plug in the firing order. So it goes: #1 Soot, #2 Clean, #7 Soot, #8 Clean, #4 Soot, #5 Clean, #6 Soot, #3 Clean.
That also means the four "inner" opposing cylinders are sooty while the front and rear are all clean. The dwell is set right, cap, rotor, points, plugs, wires all either new or check out well. My trips are mostly short but I've run it on the highway and for about 200 miles on a couple of trips. Runs pretty decently though I get a bunch of water and then lots of soot out of the tailpipes. I'm befuddled.

 

[TODD]

Cylinders 1, 4, 6, and 7 are fed by the right-hand barrels on the carb. See attached intake manifold picture from the Chassis Service Manual.

Something may be making the right-hand barrels run rich. Maybe an adjustment out of whack or a plugged vent passage etc.

Has it had any carb work done since the plug fouling started?

 

[exchaoordo]

Oh, wow, that might be it! Short answer to your question is that, yes, carb had been rebuilt by the previous owner but he had not reinstalled it on the car. So, I like the idea of the overly rich right hand barrels. I will begin exploring that variable. Stay tuned (ooh, bad pun, sorry)!