I think I have isolated my throttle problem. First, I had the carbs cleaned and balanced. This improved the problem but did not illiminate it. Next I just lowered my warmed up idle stop position. This has nearly cleared up the problem. My float valve stuck open on one carb last week, so I am in the process of getting new float valves and seats as well as refitting the pet-cock valve. One other item that I want to replace is the choke plungers. There is one on each carb, and I believe that is where the leak is actually ocurring. The part is not avail. from aftermarket suppliers, so you have to get it from Yamaha.