I was thinking of cast iron - if it cast aluminum the bronze method probably will not work but there are probably other products that will work on aluminum. Did a google search and some people are recommending Devcon which may work better than the JB Weld. I had a cast aluminum gear box off a Bolens deck that had a piece broken out of it where the seal went in - I used JB weld on it and it stuck fine to the aluminum - let it set up for a day or two before I touched it. http://gardentractor...-gearbox/page-2 post #16 I realize the carb body may get hotter than the gear box but still should work.
After looking at the picture you may want to make a new flange piece out of steel with a piece of pipe welded to it - you could put a sleeve over the pipe and your carb body for more strength - solder the sleeve to the steel pipe and then use JB weld at the carb side to seal off any air leaks once you have the carb body indexed so that it is positioned correctly and level. Another option might be some straight high temperature rad hose clamped around the carb body and a new flange piece with a steel pipe - just suggestions - someone else may have a better idea.