Problem with Kawasaki (2002) 500cc Vulcan?

I am having a problem with my motorcycle. The bike will run if I spray carb cleaner into the carb, it will start right up. It will start on its own for the remainder of the day but when it sits overnight it won't start unless I spray it with carb cleaner again. This bike had sat for years with the fuel in it, that varnished. The bike only has 4,000 miles on it, I have rebuilt the carbs (I blasted air through all of the holes in the carb) so why won't it start on its own. Once it runs it runs like a brand new bike.