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Ignition Distributor which Vacuum Port?

1773 Views 5 Replies 3 Participants Last post by  willy3oy, 
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I am following the Vacuum diagram for my 500 SEC (with 500SL Engine) and I need to run a line to the Ignition Distributor to advance the timing. My distributor has 2 vacuum ports, both of which are currently connected to the vacuum system and are almost certainly going to the wrong places. Could someone please shed some light on whether I should be using the lower or upper vacuum port on the distributor as shown in my photo. And what is the difference between the 2 ports? I have done a lengthy search but cannot find any mention of this. Thanks

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John350
The vacuum line pointing up (obvious in the photo) is the vacuum advance, and is connected to the intake manifold. There may be some sort of control valve in the path, for emission control. The other one, pointing toward the distributor body is a retard line which is definitely for emission control, and should be modulated by a device somewhere.

To get it right, you're going to need to look up the vacuum line routing diagram for your specific car in the service manual.
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John350
If the engine came from an SL, maybe you should compare the routing from the SL with the SEC. You can't just unplug some of the lines and leave them hanging...
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