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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Dec 2003 Posts: 1,061 'Bolter | | 'Bolter Joined: Dec 2003 Posts: 1,061 | If you apply suction to the vacuum advance, should it hold the pressure indefinitely or does it gradually release? I have several of these and want to bench test them.
1946 1-ton Panel
1952 1-ton Comml. W/Grain Body
| | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | If it releases it's bad, although it may work for a while.
If bad it's also a vacuum leak that will raise your idle speed and ruin your idle mixture adjustment. | | | | | Joined: Dec 2003 Posts: 1,061 'Bolter | | 'Bolter Joined: Dec 2003 Posts: 1,061 |
1946 1-ton Panel
1952 1-ton Comml. W/Grain Body
| | | | | Joined: Feb 2004 Posts: 29,767 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,767 | If there's vacuum on the advance unit at idle, you've done some very, very wrong plumbing from the carburetor. Unless you're able to suck a golf ball through a garden hose and keep it up for quite a while, buy yourself a Mityvac pump and save yourself a bunch of effort. Pump the advance to its full travel, pinch the hose off tight with a pair of smooth-jaw pliers, and see how long it takes for the vacuum to bleed off. Half a minute or more is probably OK- - - - -a few seconds isn't.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Sep 2012 Posts: 222 'Bolter | | 'Bolter Joined: Sep 2012 Posts: 222 | Jerry, Are you saying that these engines should be using ported vacuum instead of manifold vacuum? Dave | | | | | Joined: Feb 2004 Posts: 29,767 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,767 | That's the way they were designed- - - -no vacuum at idle, a gradual increase in vacuum on the advance unit through part throttle, and almost full vacuum at light throttle cruise speed. As the throttle is opened for passing or hill climbing the vacuum advance goes away to avoid detonation with the power valve open in the carburetor, leaving only centrifugal advance for pulling.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Sep 2012 Posts: 222 'Bolter | | 'Bolter Joined: Sep 2012 Posts: 222 | Thanks for the explanation Jerry. Dave | | |
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