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Old 06-12-2019, 09:28 PM
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spduffee spduffee is offline
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Unknown Vacuum Port

Hello Alll,

I can't seem to upload photos, but I think you'll all know what I am talking about. There is a manifold port in front of the carb with a 3/8"/ 1/2" hose going to the master brake cylinder. On that same port there is a small nib that I just realized is sucking in air. It has no hose on it. I stuck a piece on so I could play with it and sure enough, when I plug it, the engine runs smoother.
Looking at the vacuum diagrams, I don't see any mention of the brake cylinder, but it appears this port goes to the carb bowl, non-linear valve and the HDC CTO. This is how I found it. Is there any reason for this port not to be plumbed? I think I may have to go buy all new vacuum lines and start over.
Thanks,

Shawn
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Old 06-13-2019, 04:56 AM
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acct21 acct21 is offline
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Join Date: May 20, 2014
Location: Austin, TX
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So a lot of the vacuum line ‘spaghetti’ and various ports, CTOs, and non-linear valves are emissions-related, and not necessary for basic engine performance. Here’s a good description of the circuit in question— which manipulates vacuum to the vacuum advance pot on your distributor:

http://www.ifsja.org/forums/vb/showthread.php?t=85353

Most all of that may be safely removed, as long as the vacuum ports (like the small hub you found on the brake vacuum tree) are capped. I personally run straight manifold vacuum to the distributor; some have better luck with ported vacuum from the carb base.

Most important thing is to check all of your vacuum posts for uncapped ones or leaks.
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Old 06-13-2019, 10:00 AM
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tgreese tgreese is offline
 
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Location: Medford MA USA
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Quote:
Originally Posted by spduffee
Hello Alll,

I can't seem to upload photos, but I think you'll all know what I am talking about. There is a manifold port in front of the carb with a 3/8"/ 1/2" hose going to the master brake cylinder. On that same port there is a small nib that I just realized is sucking in air. It has no hose on it. I stuck a piece on so I could play with it and sure enough, when I plug it, the engine runs smoother.
Looking at the vacuum diagrams, I don't see any mention of the brake cylinder, but it appears this port goes to the carb bowl, non-linear valve and the HDC CTO. This is how I found it. Is there any reason for this port not to be plumbed? I think I may have to go buy all new vacuum lines and start over.
Thanks,

Shawn
Year, model equipment? Makes a huge difference in the vacuum plumbing. You could put that info in your signature file so it's in every post. Generally speaking you should have no open vacuum ports, whether they are connected to something or plugged.

The forum will not host your pictures, Put them somewhere online where they have a URL and post the link or post a hot link. You will get much better info if you figure out how to post pics.
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