[Ronbo]

Well you could try setting a small cap with some gas in it on top of the intake and see if it boils off at the same rate as the float bowls. Since your smelling gas I'd guess it's exactly what's happening.

The fill valves are pretty high up in a carb so I can't see it being a drain back issue.

The heat shield suff reminded me of a favorite carb of mine, anyone remember the Thermo-quad? These were really neat carbs that had all metering in the top and a phenolic body that kept the fuel about 15~20deg cooler.

They were standard fare on chrysler big blocks. As far as I know no one offers stuff for them anymore. Carter only offers stuff for the AFB now.