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Topic: Vacuum Connection

in Forum: C3 Fuel, Emission Control, and Exhaust Systems

Vacuum Connection

Posted: 8/18/06 4:51pm Message 1 of 7
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Lake Mary, FL - USA
Joined: 5/21/2004
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Vette(s): Just finished 2 years of Blood, Sweat, & Tears restoring my 69 Coupe. Crimsom Red, 427, vacuum removed, Shot of Steeroids, Killer Lights, 5 Speed, still working on small things but she is back on the road.

I purchased my new Holley and reading through the instructions I noticed a step that is presently not on my set up today.  It concerns the vacuum connection from the carb to the distributor.  This is not  connected on my car today.  Now I need the directions from the experts.  Do I connect the vacuum from distributor to carb when I change out my carb tomorrow?  The power booster is connected to the back of the carb so in doing this I suppose the vacuum is working on both or do I need to make a connection as well to the intake to insure I have a vacuum on the brake booster and carb? 

Thanks,Jim 




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Vacuum Connection

Posted: 8/18/06 5:16pm Message 2 of 7
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Frederick, MD - USA
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Vette(s): 1969 convertible L71 427/435 4-speed black interior
Someone needs to correct me if I'm wrong, but the vacuum advance on your distributor needs to be connected to a timed or ported connection on your carburetor. The other vacuum connections are full time vacuum and are not what you need.

Your manual for the Holley should identify the timed port. If not, see if there's information on Holley's website or another site on-line.

I'm not that familiar with Holley carbs, but others are set up that way so I'm assuming Holley is as well.


Vacuum Connection

Posted: 8/18/06 6:47pm Message 3 of 7
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Duncanville, TX - USA
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
Are you saying there is no vac. hooked up on your distributor now? If so, and it is running properly, I wouldn't worry about it. It is possible your dist. is set up for no vac. advance. If the advance mechanism inside the dist. is "fixed"(welded, pinned, etc.), then hooking vaccuum to it will do nothing, anyway.

If the vac. advance is not disabled, then you would connect the vac. line for the advance to a ported fitting, meaning it only has vaccuum above idle, none at idle. Normally, this would be a tube at the lower, front of the carb.
Check with any instructions you may have with the carb to verify the ported fitting location.


Joel Adams
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Vacuum Connection

Posted: 8/18/06 7:28pm Message 4 of 7
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Lake Mary, FL - USA
Joined: 5/21/2004
Posts: 106
Vette(s): Just finished 2 years of Blood, Sweat, & Tears restoring my 69 Coupe. Crimsom Red, 427, vacuum removed, Shot of Steeroids, Killer Lights, 5 Speed, still working on small things but she is back on the road.
Thanks, I checked this out and I know where to hook the port setting to the distributor.  There are 2 other vacuum ports, one is for the power brake port and the other is for the full manifold port.  I am assuming I need to connect the full manifold to the intake manifold vacuum and the power brake port to the brake booster.  Today the only connection I have is the one from the power brake booster to the old carb.  All other ports are plugged.   


Vacuum Connection

Posted: 8/18/06 8:47pm Message 5 of 7
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There should be two large tubes/fittings on the carb, one if the front, and one in the rear. The rear is for the brake booster. The front is for the PCV system.
You should not have to connect a vaccuum line from the carb("full mfld") to the intake...unless I read this wrong
The only connection like that that I know of is for the power valve conn., on the pass. side of the front metering block. This is of course, assuming your carb has a power valve.


Joel Adams
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Vacuum Connection

Posted: 8/18/06 9:30pm Message 6 of 7
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Lake Mary, FL - USA
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Vette(s): Just finished 2 years of Blood, Sweat, & Tears restoring my 69 Coupe. Crimsom Red, 427, vacuum removed, Shot of Steeroids, Killer Lights, 5 Speed, still working on small things but she is back on the road.

You are correct there are 2 large fittings one is marked PCV Vacuum Port on the front the other is marked Power Brake Vacuum Port on the back.  There is another one smaller on the front beside the PCV Port marked Full Manifold Vacuum Port.  All are on the lower portion of the carb.  I looked over the directions and on Holley's site but there is nothing providing any directions on how to connect the vacuum lines.

How the vacuum connections are on my car today are the following: There is a PCV mounted in each valve cover and connected to the intake manifold connection.  The power brake booster is connected direct to the back of the carb.  There is a small port on the front of the carb that is plugged.   Guessing this is the Full Manifold Vacuum.  The timed spark vacuum port is plugged as well.

I'm assuming I should connect the PCV to the PCV, the brake port to brake booster and the timed spark port to the distributor.  I will leave the full Manifold port plugged and not connected unless someone knows this should be connected.  Thanks for all the help.

Jim  




Vacuum Connection

Posted: 8/18/06 10:13pm Message 7 of 7
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Lake Mary, FL - USA
Joined: 5/21/2004
Posts: 106
Vette(s): Just finished 2 years of Blood, Sweat, & Tears restoring my 69 Coupe. Crimsom Red, 427, vacuum removed, Shot of Steeroids, Killer Lights, 5 Speed, still working on small things but she is back on the road.
OK, I think I have it now.  The full manifold port connects to the air cleaner or pump diverter (which I do not have).  So I will leave this bad boy plugged.  Thanks for the help I will get this changed tomorrow. 


in Forum: C3 Fuel, Emission Control, and Exhaust Systems


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