Glad you found the "problem", now onto the real problem. Stumble off idle. Loosen the hose clamps on the airbox side of the carb, make sure the head side ones are tight. Now try and rotate the carb body around it's axis. If you can, your instake spigots are loose and are likely the source of an airleak. Tighten to reseal. That vintage should have a slot cut on either side of the spigot that you can insert a piece of steel into to tighten them up with. If that's ok, take a look at your needles and needle jets since the tend to wear on each other, also affecting the metering.