Sounds like your idle circuit may need cleaning or adjustment. The idle circuit is the hardest one to clean because of the small hole size and there is usually no straight shot to the tiny orifice that provides the fuel. Many times, these holes don't fill with cleaner when you are soaking the carbs. Take a VERY small pin and use it to clean the two or three holes right next to the throttle butterfly plate. Also find out what your factory setting is for the Idle mixture screw and reset it. If you are able to start and run on a high idle, a good cleaning and adjustment should take care of it.
Good luck!