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 Post subject: Vacuum advance - anti pulse valve
PostPosted: Wed Oct 25, 2006 12:09 pm 
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Location: Bristol
Year of Van: 1970
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Right chaps does anyone know anything about these?

If its needed, when its needed? :?:

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PostPosted: Wed Oct 25, 2006 3:26 pm 
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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.


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PostPosted: Wed Oct 25, 2006 3:29 pm 
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Yea thats it. It was just a suggestion that someone told me about.

You apparently don`t need to fit one, but if there are some issues with the running then, this could help as it smoothes out the vacuum once it has been used in early revs.

Probably just another gadget that you don`t really need. 8)

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PostPosted: Wed Oct 25, 2006 3:58 pm 
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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.


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PostPosted: Wed Oct 25, 2006 4:11 pm 
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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.

Probably end up selling it on flea bay! :wink:

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PostPosted: Wed Oct 25, 2006 5:12 pm 
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Where do you get them from? I've never bothered to find them.


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PostPosted: Thu Oct 26, 2006 9:13 am 
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You can get them from http://secure.visav.co.uk/avshop/produc ... witem=1928

I spoke to the guy there who works on all the engine bits and he says that you don`t really need em unless there is some tuning issues. Worth having incase you get stumped for ideas though 8)

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PostPosted: Thu Oct 26, 2006 10:03 am 
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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.


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PostPosted: Thu Oct 26, 2006 10:08 am 
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I agree, it would seem to be better for the big old carbs. Good idea with the copper pipe, may have to nick that one! 8)

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viewtopic.php?f=33&t=42483
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