When you sync dual carbs on a Bug, do you disconnect the linkage between them so they operate independently? That's the key when sync the dual SU carbs on the Mini.

That's how you're supposed to synch them at idle on VW's too. Then you synch them at part throttle with the linkage attached.

How do make sure you do not have one dominate over the other when they are linked together?

You make sure that when you crack the throttle that both carbs idle speed screws are the same distance from their stops