[patrickt]

... and move the soaky, soapy rag up against anything on the outside of the carb too. Press it against the idle mixture screws, the little rods that come out of the sides of all carbs, any screw that you see, bolts, etc. on the sides of the carb. Basically anything on the outside of the carb that you can squish the wet rag against do it. That should tell you if the problem is on the outside or not -- it could be a really small hairline crack that you can't even see.