I know that the gas isn't seeping back down into the fuel pump. It is a brand-new pierburg pump, for one thing. But more importantly, I checked it. I had my brother-in-law crank the engine while I held the hose into a glass jar, first thing in the morning. The gas was coming out very strongly.

What I did to the choke was simply to replace the O-rings. I didn't completely disassemble the carbs and clean them, so perhaps there is gunk in there. But what makes me think that there isn't is the fact that once the car is warmed up pulling out the chokes makes the RPMs shoot way up. So the choke is definitely supplying extra fuel. And also the rough idle which was present before I replaced the O-rings in the chokes is now gone, so that makes me think it is working well.

Greg