that connector pipe that goes between carbs has an o-ring on both ends and this is probably your problem, pull the carbs and replace the o-ring while the carb rack is out you can hook up a fuel supply line that is gravity feed.i use a 2 liter bottle with the bottom cut out and a small line thru the cap, sorta looks like an I V ,hook this to the rack and pour some fuel in the bottle once the bowls fill you'll be able to check for leaks, you can also do this when you first pull the carb rack to see if it is the o-ring js the problem