Vacuum question.
Thread Starter
Burning Brakes
Joined: Oct 2003
Posts: 1,097
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From: Olive Branch MS
St. Jude Contributor
Vacuum question.
I have noticed recently when I turn off the car that I hear a hiss from the front for just a second or two. Could this be a vacuum leak at the headlights? If it is could it be affecting performance during run time? If so what is the best way to trace it down. Thanks.
Also noticed while I was working on advancing dist yesterday that timing does not advance at all when vac advance is hooked back up. Is this normal? And I did replace the vac advance canister in the dist.
Also noticed while I was working on advancing dist yesterday that timing does not advance at all when vac advance is hooked back up. Is this normal? And I did replace the vac advance canister in the dist.
Last edited by brooksman9; May 17, 2005 at 11:34 AM.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by ruby76
Yeah, but wouldn't the check valve prevent any engine running problems? or not? But I do think it is vacuum leak.
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Originally Posted by brooksman9
I have noticed recently when I turn off the car that I hear a hiss from the front for just a second or two. Could this be a vacuum leak at the headlights? If it is could it be affecting performance during run time? If so what is the best way to trace it down. Thanks.
Also noticed while I was working on advancing dist yesterday that timing does not advance at all when vac advance is hooked back up. Is this normal? And I did replace the vac advance canister in the dist.
Also noticed while I was working on advancing dist yesterday that timing does not advance at all when vac advance is hooked back up. Is this normal? And I did replace the vac advance canister in the dist.
BigBlockk
Later.....
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Burning Brakes
Joined: Aug 2002
Posts: 1,146
Likes: 10
From: Scottsboro Alabama
Originally Posted by brooksman9
I have noticed recently when I turn off the car that I hear a hiss from the front
Patrick, it might be one of those badass Mississippi cottonmouths taken up residence.!!
Drifting
Joined: Sep 2001
Posts: 1,427
Likes: 1
From: Boxford Mass
The hiss could be coming from a faulty actuator relay. The aftermarket units tend to leak -- I went through two of them before I ponied up the money for an original piece.
It hissed for about 5 or 10 seconds until the vacuum was lost in the system.
It hissed for about 5 or 10 seconds until the vacuum was lost in the system.
Drifting
Joined: May 2005
Posts: 1,909
Likes: 6
From: Lake Arrowhead - Georgia > 72 Base Coupe & 74 BB Roadster
Check your valves....sorta !
On my 72/350 this worked - Check the 3 relay vacuum switches (or 2 if 73 or later) that relay positive or negative vacuum to each headlight actuator or the wiper door actuator. They will still work even if they are suckng air in the most bottom seal. If they suck air in the bottom it can affect the mixture, especially at idle. Two are under the nose and one is under the passenger front fender. Mine leaked so bad that the engine idled so rich, it would carbon the plugs til it would not even run. I replaced all three - and it idles properly again. I still have a "leak down" after shut down near the vacuum tank, but have not isolated it yet.
Thread Starter
Burning Brakes
Joined: Oct 2003
Posts: 1,097
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From: Olive Branch MS
St. Jude Contributor
Originally Posted by BigBlockk
Your advance won't move if you have it hooked up to ported vacuum.
BigBlockk
Later.....
BigBlockk
Later.....
Drifting
Joined: Sep 2004
Posts: 1,532
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From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
I thought you were supposed to have "around" 16* initial timing, 20* mechanical by 2800rpm. 16* + 20* = 36* at 2800 rpm. Then the vacuum advance will add another 16 or so on top of that.
Race Director
Joined: Sep 2004
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by ruby76
I thought you were supposed to have "around" 16* initial timing, 20* mechanical by 2800rpm. 16* + 20* = 36* at 2800 rpm. Then the vacuum advance will add another 16 or so on top of that.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by ruby76
Hey bobs77vet, did you ever see any MPG gains, or are you too busy putting your foot in the throttle!!!!