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Re: [T3] Vacuum Advance and setting ignition timing


On 20 Nov 2002, at 18:10, jim wrote:

> I was able to check where the vacuum hose to the dizzy is connected and it
> is attached at the plenum/intake air distributor on the underside close to
> where the air cleaner elbow attaches.  So it looks to me like its connected
> where the retard hose should go; however, I don't know exactly where the
> Throttle Body is.  The Throttle Valve switch is also connected to the plenum
> on the side so I need a little clarification for where the vacuum adv. hose
> SHOULD be connected.  It the throttle body underneath the plenum?  And also,
> where should the vacuum advance hose attatch.  Sorry for the basic question,
> but it'd be great if a big part of the solution were as easy changing where
> the hose attaches. 

Type 3s don't have a separate throttle body, it is just part of the intake air 
distributor (IAD), that big thing in the middle of the top of the engine. I agree 
that you have your vacuum advance hose connected to the retard vacuum 
port, which comes out of the lower left side of the IAD, just downstream of 
the throttle butterfly valve. The advance vacuum port is on the TOP left of the 
IAD, just downstream of where the elbow from the air cleaner connects, or 
upstream of the throttle valve. On 72-3 cars this connection is often a right 
angle connection and it may be hidden under a bracket that holds a throttle 
valve dashpot (shock absorber.) 

> I looked through the Bentley for a diagram of the hoses but there weren't
> any. However, it did say removing the vacuum retard hose while the car was
> running would move the timing/advance 15-18mm which is pretty close to what
> my car does when I remove the vac. hose. 

Yes, but you have it connected to the vac adv, so the vacuum there at idle 
should make the timing marks move to the left (advance) when you attach 
the hose and move to the right (retard) when you remove the hose. This is 
backwards from what the vacuum retard would do, which is logical when you 
think about it.  

For these distributors, more vacuum gives more vacuum advance and more 
vacuum retard (for those distributors which have the vacuum retard.) They  
don't both get the same vacuum at the same time.  

-
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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