Join Date: Nov 2010
Location: Mulberry, FL. USA
These are really very old bikes, and you don't say if it had been sitting for long time. If so, it probably needs carbs cleaned for sure. Thht might help the sputtering
...idling changing does sound like a possible vacuum leak, but there is not much to the vacuum lines, assuming the carb boots are in good shape. Don't know much about your particular bike, but in general vacuum operates the fuel petcock, and the Kawasaki "Kleen" system for polution (air into the exhaust valves, through the valve cover). Because the bike is very old, all of this could be sources of leaks, but is not very difficult to find it.
......don't promote pollution, but the 'Kleen" system could also be eliminated for simplicity.