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Discussion Starter #1 (Edited by Moderator)
Where is the vacuum section on this website? Sorry if I put this thread in the wrong group.

On a 1972 manual transmission intake manifold there is the screw port for the brake booster vacuum tree and below that there is a small tube that projects out of the manifold. OGTS calls it port B on their Where do the hoses go document dated 7/4/2012. They also state that the port B gets plumbed to the valve cover.
My question is, "Is this port open to the inside of the intake manifold?" I can not blow through mine nor can I see that the tube penetrates the manifold. I tried to put a small piece of solid wire through to unblock it but it would not go through. I dont want to drill it out if it is not supposed to be.
If this is supposed to be open to manifold vacuum then mine is completely blocked.
:confused:
 

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Can Opeler
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The big port goes to the brake booster. The tiny port on that same tree goes to the valve cover. It is a metered orifice and is open to the inside of the valve cover. The metered orifice is a .060” hole. A 1/16” drill bit is close enough to clear it.

The B port below the tree goes to vacuum retard on the distributor the port near the bottom of the vacuum canister.

The port on the carburetor goes to the other upper port on the distributor for vacuum advance.
 

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Pedal Smasher
1973 Opel GT
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The B port below the tree goes to vacuum retard on the distributor the port near the bottom of the vacuum canister.

The port on the carburetor goes to the other upper port on the distributor for vacuum advance.
Unless you don't want to use the stock configuration, and use manifold vacuum advance. You wouldn't use port vacuum or the retard port on the vacuum canister. Getting into why you'd do this is a long debate over port vs manifold vacuum advance, and which one is better.
 

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The big port goes to the brake booster. The tiny port on that same tree goes to the valve cover. It is a metered orifice and is open to the inside of the valve cover. The metered orifice is a .060” hole. A 1/16” drill bit is close enough to clear it.

The B port below the tree goes to vacuum retard on the distributor the port near the bottom of the vacuum canister.

The port on the carburetor goes to the other upper port on the distributor for vacuum advance.
I just went through this, and Knorm65's advice is spot-on. I have a '69 engine in my '71GT that has manual gearbox. But the engine had an intake manifold from a later model Opel with the additional outlet for the emissions device that had been capped off, and it had an additional port for the vacuum line running to an automatic transmission's modulator valve. The fact that the exhaust manifold had a broken attachment ear led me to decide to change the entire unit out. With Jim's assistance in New Hampshire, I acquired enough pieces to put a more correct unit together. But still a bit confused, I went directly to Gil for clarification as to the proper hookup, and he spelled it out exactly as Knorm65 lays it out, although I do not understand fully "vacuum retard on the distributor the port near the bottom of the vacuum canister." This may be a reference to the design of the distributor's vacuum system, but in my case, the distributor has two distinct vacuum chambers, one of which, in the front, is the advance, and the one in the rear is the retard. In either event, the "B" port connects to the retard port on the distributor while the advance port connects from the carburetor's port. The line from the valve cover connects to the metered port on the tree (clearly visible in the picture below).

The first picture is the tree that was on the car, that has been replaced -- note the "B" port extends from the top of the tree and that the emission connection is where the "B" port is found on earlier models. The second picture is the distributor with the two separate vacuum chambers.
 

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I just went through this, and Knorm65's advice is spot-on. I have a '69 engine in my '71GT that has manual gearbox.
You also have a distributor with two vacuum canisters. The more common distributors (70 thru 74) have one vacuum canister with two vacuum nipples. Connect to the largest vacuum nipple for vacuum advance. The smaller nipple is for vacuum retard, an emissions thing.

Harold
 
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