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| | | | Joined: May 2001 Posts: 7,438 Extreme Gabster | | Extreme Gabster Joined: May 2001 Posts: 7,438 | On my '54 GMC 248 I disconnected the tube to the vacuum advance from the carburetor and checked the reading there. The manifold port has a hose to the power brake booster. I left it connected.
The book says I should get a reading of 18-24. I get 9.
Which port should I be checking? Should the other port be capped? | | | | | Joined: Jun 2008 Posts: 1,388 Shop Shark | | Shop Shark Joined: Jun 2008 Posts: 1,388 | You want to measure the vacuum from the intake manifold port. This is where you put the gauge for tuning. You can leave the dizzy vacuum connected for this. | | | | | Joined: Jul 2007 Posts: 293 Wrench Fetcher | | Wrench Fetcher Joined: Jul 2007 Posts: 293 | You should be checking vacuum on the manifold port. I know because I made the same mistake. Plug the other port or keep it connected to your distributor. | | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | There should be an outlet for w.wipers. Use that one for vacuum testing.
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: May 2001 Posts: 7,438 Extreme Gabster | | Extreme Gabster Joined: May 2001 Posts: 7,438 | Thanks guys. I'll check the manifold port when I get back to it. | | | | | Joined: Feb 2004 Posts: 29,742 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,742 | The distributor port should get zero vacuum at idle, and it should increase as the engine is revved up. I doubt if it will ever get quite as high as full manifold vacuum. For tuning purposes you need to monitor the vacuum at the manifold, not the distributor port.
Jerry
Last edited by Hotrod Lincoln; 01/06/2010 6:14 PM.
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| | | | | Joined: Dec 2006 Posts: 1,154 Shop Shark | | Shop Shark Joined: Dec 2006 Posts: 1,154 | We check the vacuum at the manifold wiper port and we disconnect the vacuum line to the dizzy and plug it on our 235 for timing. This method as per my uncle. | | |
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