That fuel bowl looks like cast zinc and cannot be soldered.As R413 states, there's a seal under there. You can try tapping with a tiny hammer to tighten the seal, or you can heat it up (which will destroy the seal) and solder the metal cap to the fuel bowl casting. But replacement fuel bowls are cheap.
Zinc can be easily soldered, but of course due to its low melting point you wouldn't use ordinary 50/50 solder. Low temperature solders are available at sheet metal shops for use on galvanized steel, or Muggy Weld can be used. You Can Solder Zinc and Zinc Die Cast with Super Alloy 1 Zinc Repair Kit -.That fuel bowl looks like cast zinc and cannot be soldered.
Mike
I stand corrected! I was only thinking about the heat required to melt 50/50.Zinc can be easily soldered, but of course due to its low melting point you wouldn't use ordinary 50/50 solder. Low temperature solders are available at sheet metal shops for use on galvanized steel, or Muggy Weld can be used. You Can Solder Zinc and Zinc Die Cast with Super Alloy 1 Zinc Repair Kit -.
Neither do cathedral bowl HolleysEdel/Carter carbs do not have that problem....