Have you verified the float level? Is your needle valve sticking? When the engine is idleing and you spray some starting fluid across the top of the oval opening, is there any difference in speed? I still suspect a leak somewhere. Peruse the diagrams again and double check all the gaskets and seals. A customer of mine had the same problem with his twin carb 220s and as soon as he changed the paper gaskets, the problem disappeared. Gently spray the starter fluid around the carb until you find the leak. Let us know your findings.