Stalling Issue (Slant Six w/Holley 1920 Carburetor)

I've seen references to advancing ignition timing, but this is the first time I've read why. Why does crappy gas = advanced timing? Is there an indicator for too much advance besides ping?

I thought too that someone that knows more than me (okay anyone) would have mentioned the exhaust heat flapper by now. No? :poke:
I made the poor assumption that ignition timing and a working heat riser were already something that had been set and in good shape. Yes, the heat riser can effect cold driveability to a certain extent, mainly in a cold climate. It has very little effect here in San Diego, so, that isn't something that immediately comes to mind.