Vacuum - How Long ?
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
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From: North Texas
Vacuum - How Long ?
Ok after I shut the car off, how long should the car hold vacuum after the 1 way check valve?
I just replace the two head light relays and the head lights work but I think I'm suppose to have vacuum at the surplus tank after the car shuts off and my slowly drains away....
I've checked the 1-way valve and it works fine.
I just replace the two head light relays and the head lights work but I think I'm suppose to have vacuum at the surplus tank after the car shuts off and my slowly drains away....
I've checked the 1-way valve and it works fine.
Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
i know of no one whose car holds vacuum after its shut down....
i would not worry about this.. too many areas for small leaks.
i would not worry about this.. too many areas for small leaks.
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
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From: North Texas
Bob, That's kinda what I was thinking.
What I'm concerned about is when I by-pass the vacuum accessories and plug the port on the manifold, you can hear the engine pull down. Does that make sense?
So do I just tune the Carb with the minor leak?
What I'm concerned about is when I by-pass the vacuum accessories and plug the port on the manifold, you can hear the engine pull down. Does that make sense?
So do I just tune the Carb with the minor leak?
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 1970-Bronze
Bob, That's kinda what I was thinking.
What I'm concerned about is when I by-pass the vacuum accessories and plug the port on the manifold, you can hear the engine pull down. Does that make sense?
So do I just tune the Carb with the minor leak?
What I'm concerned about is when I by-pass the vacuum accessories and plug the port on the manifold, you can hear the engine pull down. Does that make sense?
So do I just tune the Carb with the minor leak?
well we maybe talking about two different situations.....residual loss of vacuum vs. out right leak....
if there is an outright leak you need to remedy this....if you are talking about a residual loss of vacuum i would not worry about it. what do you mean by "pull down". a decrease in idle rpm?
edit ok i think i am following you....sounds like you have vacuum leak you need to find....disconnecting and plugging the vacuum accessories port should not decrease the idle unless you have a leak which you need to fix.
Last edited by bobs77vet; May 16, 2005 at 09:58 AM.
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 990
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From: North Texas
Exactly. I can hear it pull down the motor "slightly" when I cap the manifold port instead of connecting the accessories.
Great - I wonder if I should just start replacing hoses while I'm at it.
Great - I wonder if I should just start replacing hoses while I'm at it.
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 1970-Bronze
....Great - I wonder if I should just start replacing hoses while I'm at it.
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Instructor
Joined: Aug 2002
Posts: 203
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From: Anaheim Caleefornia
My '69 holds vacuum for about 3 minutes following shutdown. Then I can hear (in a quiet garage) the outside air damper slowly being pulled open by its spring.
I guess I am lucky. My vacuum system has always worked well and has been largely trouble free. Knock on wood.
Best of luck to you,
SharkPilot
I guess I am lucky. My vacuum system has always worked well and has been largely trouble free. Knock on wood.
Best of luck to you,
SharkPilot
Melting Slicks
Joined: Jul 2002
Posts: 3,128
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From: Deltona (son of Deland and DAYTONA) FL
I added an extra vacuum reservoir when I had my 383. On that motor, there was only one vacuum line running from the manifold to the tank, which had a check valve. Any vacuum leaks in the car are isolated from the motor because of the check valve in the tank.
My L48 pulls much more vacuum and I've since added vac advance to a port on the carb. Everthing else still runs through that tank.
My L48 pulls much more vacuum and I've since added vac advance to a port on the carb. Everthing else still runs through that tank.
Thread Starter
Burning Brakes
Joined: Nov 2003
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From: North Texas
Originally Posted by isosceles
On that motor, there was only one vacuum line running from the manifold to the tank, which had a check valve. Any vacuum leaks in the car are isolated from the motor because of the check valve in the tank.
The 1-way check valve prevents the accessories from pulling from the engine but not from leaking vacuum while it's running. The leaks would still bleed off vacuum while it's running.
Race Director
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by 1970-Bronze
When the engine is running, how are you isolating the leaks in the car?
The 1-way check valve prevents the accessories from pulling from the engine but not from leaking vacuum while it's running. The leaks would still bleed off vacuum while it's running.
The 1-way check valve prevents the accessories from pulling from the engine but not from leaking vacuum while it's running. The leaks would still bleed off vacuum while it's running.
??? not sure what you mean? if you have a leak in a vacuum hose it will increase your idle speed regardless of the check valve? take the hoses off individually and plug them watch to see when the idle goes to where it should be ....that will point you to the problem area
