When I bought my America, it had been sitting for 2 years without being started. When we started it, it did exactly the same thing (one carb, bad idle etc). I realised that he hadn't started it prior to me coming around to look at it. It also leaked fuel from the overflow tube.
I bought it and before leaving his place pulled the carbs and cleaned them out (blew the jets, used a wire from a wire brush to run throuh them etc). I also changed the oil!
Runs like a demon now and hasn't missed a beat since.
