My 1966 chevelle ss is leaving black soot on the ground after a cold start. This only happens on the drivers side. The carb. has just been rebuilt. My car has a 396/360 engine with the original holley carb. and holley intake manifold.

Could be a plug or ignition problem. If the cyl doesn't fire every time carbon will build up and come out when it does fire.

Maybe you have a fouled plug on that side?

I will vote ignition as well, check there first. Plug, wire, boots, cap etc.