Triumph Vitesse manifold vacuum. 

Fitted Mikuni HSRs to my 2L Vitesse, had to disconnect the engine breather from the inlet manifold in order to remove an initial lean spot on initial throttle opening. That made the mixture good but the additional vacuum now seems to be too much for the Standard Lucas Vacuum Advance which is permanently on full advance causing pinking on acceleration. The VA take off on these carbs is manifold vacuum which causes the VA to feel even greater suction than the standard ported take off. This is my manifold vacuum with Vacuum advance disconnected.