1 The petcock has to be hooked to manifold vacuum. There may be a port below the throttle plate on one of the carbs that provides the vacuum to operated the petcock. At least that is the way it's hooked up on my ZN700.
2 I'm sure it tees into both carbs.
Welcome to the site. I'm 75, so don't feel like you're the old guy!
1985 Kawasaki ZN700 Shaft, 4cyl
1989 Yamaha Venture Royale
2007 Yamaha Royal Star Venture