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74 tii distributor - best practice


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Just recently got my hands on a 74tii that is mostly original. The PO has disconnected the deceleration valve and associated vacuum tubing, pugged the port on the plenum but left the nipple on the distributor open. 


Why do people do this? IE what is the desired effect? (I haven't seen this question(s) answered in the search)


Trying to determine what to do IE reconnect the tubing or leave as is. Should the vacuum retard port on the distributor be left open to atmosphere or should this be plugged?








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I'm just becoming familiar with the Tii engine myself, but according to Mike Macartney in the '02 Restoration Guide, Tii distributors use mechanical advance only, hence no vacuum connections.  This is the  distributor on my '72 Tii - no vacuum bell. Hope this helps.


1972 BMW Inka 2002Tii  ?

1974 BMW Turkis 3.0 CSi ?

1972 MBZ Weiss 280SE 4.5 

2006 BMW Cobalt 530i (38,700 m original)

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On 5/13/2017 at 7:26 AM, Anthony said:

Should the vacuum retard port on the distributor be left open to atmosphere or should this be plugged?

You can plug it to keep it clean, but it will not affect your timing in any way.

Around here, mason bees plug little holes for you, though the vacuum nipple is smaller than the 1/4"-5/16" hole that they prefer. :ph34r:


Based on my reading here, the 72-73 tiis had mechanical only distributors.


In 74 they made a change to the cone in the Kfish, which had different timing needs.  The 74tii had a vacuum retard pod, like you are describing.


I don't know whether the function of the pod was part of the emissions package and otherwise 'unnecessary', or if the retard feature is needed to achieve the proper advance curve.  Sorry.  I am eager to learn the answer too. 


It would be interesting to see the advance curves with and without the vacuum pod.

Do you have a timing light with variable advance?



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