Take the carb off, apply RTV between the carb body and o-ring, also remove the carb screws and seal them up good with RTV and replace them, put the carb back on and press hard, and tighten the screws, that should take care of the air leaks.

RTV is gasket maker available at any auto parts store. You got air coming into the carb, more than likely from the 2 sources listed above, so your engine is getting just enough air and fuel that it doesn't want to shutdown.