just wondernig if my choke pull down unit is connected right.
The vacuum tube from the base of the carb comes to the lower port on the unit. The upper port on the unit connects to the green ball and the inlet manifold (via the one way valve).
The one way valve is set so as to allow vacuum to bleed into the manifold piping from the vacuum reservoir, ie the vacuum in the green ball cannot be higher than that of the manifold
the reason I ask is that the unit seems to leak vacuum like a sieve but still operates correctly, odd and I can't work out whether its broken, fitted wrong or fine
many thanks
Drew
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There is a huge thread here on Pierburg carbs - you'll probably find something useful in there.
www.honestjohn.co.uk/forum/post/?f=4&t=8799
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Dump it and fit a Weber!
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I think your one way valve is fitted the wrong way round. Its purpose is to hold the vacuum created by the manifold into the sphere. The vacuum hoses used by VW deteriorate badly, I replace them routinely. Is it the choke pull-down unit leaking? If so replace it but I suspect a split/porous hose somewhere.
Andrew
Simplicate and add lightness!
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Hi Andrew,
I saw on another thread where you said that the under-bonnet diagram was incorrect as to the 'way round' of the one way valve. I was just wondering why you thought that as it makes sense to me as it currently is (ie as in the diagram) but am prepared to bow to expert advice.
I will check the pipes but I can hear the vacuum leak from the choke unit itself, I take it from your reply that this is not normal.
Actually, I recently replaced the majority of the vacuum pipes on the back of the carb and those for the green ball, the one from the carb to the choke pull-off was one I left though.
thanks for your advice, you're the first person I've spoken to who seems to understand how the 2e2 works
my thoughts on the one way valve are that: the vacuum downstream of the choke unit (ie in the reservoir) is limited to the vacuum in the manifold, thus this downstream vacuum properly controls the second position of the choke pull-off. When manifold vacuum falls the one way valve opens and the reservoir can empty, thus the choke pull-off will return to its first open position, but will do so slowly. No??
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I have never quite understood the logic of the sphere, VW seem to be the only people who use it. Vauxhall use a similar unit and the upper port is connected to a thermal switch. This prevents the pull down from operating for a few seconds when really cold to prevent stalling on startup.
The valve should be positioned so that the system is isolated from the manifold when the engine is off, ie the sphere is evacuated and the vacuum is maintained for a while after the engine is stopped. If the valve is the other way round the vacuum will only build up slowly and there would be a risk of over choking and stalling.
Andrew
Simplicate and add lightness!
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OK well I've had a good think about this and have swapped the valve direction round so vacuum is retained in the sphere.
My reason is this:
for a hot start (after the engine has been off for an hour or so) the pull down unit will need to operate pretty much straight away to prevent over choking and stall. The sphere therefore retains some vacuum to help this and ensure the pull down opens to its second position quickly.
for a cold start, the vacuum in the sphere will have decayed allowing the pull down to operate at its first position for 10-20 seconds whilst the vacuum is restored.
This is what Andrew said above but I have now seen it in action on my car (only yesterday though) and it seems to be true so far.
ta
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