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Discussion Starter #1 (Edited)
I'm only pulling between 15-16". While searching around for possible problems, I noticed something interesting with my brake booster:



Is that second tube supposed to be connected to something? Plugged? With the vacuum gauge attached I covered the hole with my finger and vacuum jumped to around 17" (although the engine bogged a little so I'd imagine retuning the carb, checking the timing it might pull a little more).

Thoughts?

Edit: BTW, '68 289
 

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I have never seen a brake booster like that, but then again I've never owned a '68. Any unused vacuum fittings should always be plugged, though. An open fitting in a vacuum system is like a short to ground in an electrical system. You will probably be able to lean your mixture a bit afterwards.
 

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Discussion Starter #4
Thanks for the quick feedback! I figured it shouldn't just be open, but I wanted to make sure it doesn't have some special purpose that I'm neglecting. I bought the car about 6 months ago, replaced the intake manifold and carb about a month ago, and have actually been driving it. I just noticed the low vacuum when I was tuning the carb and finally got around to asking :)
 

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Thanks for the quick feedback! I figured it shouldn't just be open, but I wanted to make sure it doesn't have some special purpose that I'm neglecting. I bought the car about 6 months ago, replaced the intake manifold and carb about a month ago, and have actually been driving it. I just noticed the low vacuum when I was tuning the carb and finally got around to asking :)
On some cars the auto trans modulator was connected there. Cap it.
 

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if its sucking air plug it
 

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Plug all the vacuum ports and see if your vacuum improves. And dial in more than 6 degrees initial timing. That will raise your vacuum.
 
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