part throttle bog/hessitation/backfire

The worst cases I've seen of this was "some girl" who had a late 60's Chev inline 6 pickup, with headers. Installing headers removes the carb heat completely. Of course the "smog" snorkel heat had been removed, and I finally built a "stove" on the header.

The thing was almost completely undrivable in 30s--40's F weather, especialy when wet.

That's beginning to sound like "what this is." Once saw ice on the bottom of a Corvair dune buggy intake.........aftermarket manifold on a hot San Diego day

It's called "refrigeration effect." When you run air at high speed through the carb venturi, that cools the air.........just like your air tools. Water in the air causes more cooling. Then you invoke gasoline into the mix, and this causes MORE cooling.

Google "carburetor icing" on aircraft. THAT has crashed aircraft.