This is the thing. The stock dissy only uses VAC advance at low revs, once the butterfly on the carbs is fully open the vacuum in the manifold has dropped off, so the dissy relies on the centrifugal advance. As both carbs are sync'd and balanced, and connected by a balance pipe between the manifolds, the vacuum will be the same in both manifolds, so you only need run VAC off one of them, so what is the need of an anti pulse valve.