I don't really have the experience to help you but maybe you'll get something from what my experience was when i got my bb chevy running.
Before I had a timing light I set the timing as best I could, it was running well and it turned out to be almost 50 degrees advanced WITHOUT the vacuum advance. I rolled it back and it ran like crap and would barely keep running without my foot on the gas.
One time while I was trying to start it I was getting fireballs out the carb too (I didn't have the air cleaner on at this point though). I think the fireballs were because I flooded the hell out of the carb while I was setting up my gas pedal the night before (basically I emptied the floats while testing the linkage until I got it right).

At any rate, the engine was hard as hell to start and once it did it wouldn't idle until it was FULLY warmed up. I was getting real frustrated.

Long story short, after some tweaking of the carb and choke and timing it is working well now. My timing is set at 15 degrees static and with the vacuum hooked up it bumps it up to 25.
One thing for sure, it idled the best when it was way up before I got that timing light.

This probably doesn't really help you but there is hope.
I wish I got a picture of that fireball, that's for sure.