I think (but don't hold me to it) that the secondary only opens up under load. It should shoot fuel from the jet as you press the pedal all the way to the floor. With your rig running have someone press the pedal to the floor and carefully look down into the carb. It should start squirting fuel into the second butterfly under load. At least that's the way that most of the V8 carbs I used to work on worked. Maybe someone else has a better tip. Good luck!