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Discussion Starter #1
When I purchased my 69 Z/28 the Booster line was hooked to the Holley 780 base on the passenger side and the PCV line was on the back of the stock Winters intake. Vacuum was at 8-9 HG. Was told that was backwards so changed lines around and idle jumped up by 400rpms. Vacuum can numbers jive for that engine but have installed a Pertronix III to try to maintain stock look. Haven't re-checked timing but that's next.
 

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Sounds like you got it correct. Manifold vacumm to the distributer vacuum can is what you want not ported. Better idle and the engine runs cooler.
 

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The booster does go to the intake, and the pcv goes to the big port on the passenger side of the carb base plate if it's a 780. It should not have effected the idle. What is your idle? Mine is happy around a grand. Spray some carb cleaner around the base plate and your vacuum hoses when it's running and warmed up. If the idle changes you have a leak.
 
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Discussion Starter #5
The booster does go to the intake, and the pcv goes to the big port on the passenger side of the carb base plate if it's a 780. It should not have effected the idle. What is your idle? Mine is happy around a grand. Spray some carb cleaner around the base plate and your vacuum hoses when it's running and warmed up. If the idle changes you have a leak.
Engine is happy idling at 850. But last 2 journeys had to cool down before it would start which wasn't happening before changes.
 

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What you changed should make no difference in the engine. They were both pulling vacuum before. I would check to see if the distributer moved a little. Mine never idled that low. Grand is my sweet spot.
 

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Keith is correct with the vacuum connections for PCV and brake booster. When you said your Idle jumped by 400 rpm I assumed you changed from ported to full manifold vacuum for your distributor. Make sure it is connected to full manifold vacuum. I have a 4346 780 Holley and connected my advance can to a T fitting on the manifold for full vacuum shared with the brake booster.
 

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Keith is correct with the vacuum connections for PCV and brake booster. When you said your Idle jumped by 400 rpm I assumed you changed from ported to full manifold vacuum for your distributor. Make sure it is connected to full manifold vacuum. I have a 4346 780 Holley and connected my advance can to a T fitting on the manifold for full vacuum shared with the brake booster.
Thanks I have the same carb which has been freshly rebuilt but my advance can is connected to the port at the base of the carb. Will have to change the fitting on the manifold.
 

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Port at the base of the carb should be full manifold vacuum. Ported vacuum is normally taken from the side of the metering block.
 

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I agree with the brake booster pulling from the manifold and the PCV routed to the carb base.

Im a little confused... Why are we routing manifold vacume to the distributor? You would want to run ported vacume to the distributor otherwise you'll have too much advance at curb idle. I think your idle changed because your advancing the timming plate in the distributor with full manifold vacume at an idle. Am I overlooking somthing?
 

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If I recall GM put the distributer advance line on the metering block. I'm getting old. I may have it backwards. 🤔
 

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I agree with the brake booster pulling from the manifold and the PCV routed to the carb base.

Im a little confused... Why are we routing manifold vacume to the distributor? You would want to run ported vacume to the distributor otherwise you'll have too much advance at curb idle. I think your idle changed because your advancing the timming plate in the distributor with full manifold vacume at an idle. Am I overlooking somthing?
The reason manifold vacuum is better than ported is here: http://www.camaros.org/pdf/timing101.pdf
 

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Ported vacuum to the distributor was used for emissions. The timing was also retarded for the same reason. Factory 69 396. 4 degrees BTDC
 

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The Timing 101 article referenced above tells you all you need to know. Go with full manifold vacuum to the distributor advance and your car will run a whole lot better. Also search for Dave Ray's information on positive stops for the vacuum advance.
 
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