Another question that needs to be asked. Is the distributer vacuum advance, or mechanical. i have run into this problem before when my 69 truck was carbed. Ended going through the entire fuel and ignition system to only find that the advance diaphragm on the distributer had failed. It had hardened up from the fuel vapors. And another thing i have noticed with alot of carbes on the market despite all the power valves and such, if u get 1 up fire through the carb it never runs right again unless u rebuild.
There was two other times this happened to me and found that the advance springs had stretched and were worn out.
Hope this may help.