I'm new to the site and look forward to reading and asking questions. I bought a 56 thunderbird with a 312 4 barrel  and it runs ok but when first started up 

Welcome to the site.  You'll probably get several possible fixes to the problem.  A carb overhaul probably wouldn't be a bad idea, however one simple thing to check is the large (about 1") brass plug at the back top of the carb.  It sees full fuel pressure and when it leaks fuel runs directly into the secondary throats.  If the outside of the bowl gets wet when the car is running, then the plug is leaking.  It is not unusual for them to loosen and leak.  If it is leaking, try tightening the plug, just be careful not to over tighten, it is screwed into pot metal.  A rich mixture will cause an accumulation of carbon deposits in the exhaust system causing the soot you see on the wall.

John - "The Hoosier Hurricane"

Thanks Hoosier ,