Is this for the VAC for your dual ICTs? Someone suggested one for my dual FRDs, but the Dell'orto Tech book dosen't refer to one so I haven't bothered. I'm just running a VAC line direct from the left carb to the dissy. I was lead to believe that you only need to run an anti pulse valve if your VAC signal is taken from both carbs.
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.
As far as I am aware its used to help the vacuum and holds it to copy the other 3 and when it reduces it slowly comes back and balances it out, as opposed to rushing straight back in, which can lead to popping etc.
I think that my plan is to fit the carbs, get it tuned and rolling roaded and see what happens. I may get one as its only a tenner, so that if i need it
Ive got it.
I reckon they are best used with big dual double barrel carb setups, like Weber IDFs or Dell'orto DRLAs, where the vacuum in the manifold is to big for the small VAC can on a stock VW dissy.
What I've done is made my VAC line out of small bore copper pipe to replicate the length of the original VW VAC and as the size of my carbs is the same as the stock VW one it should all operate correctly.