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Topic: Carb Vacume Question

in Forum: C3 Fuel, Emission Control, and Exhaust Systems


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Carb Vacume Question (1/15)
 5/20/08 8:30pm
bio11
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Oklahoma City, OK - USA

Vette(s):
1972 LS5 Convertible,Auto.Targa Blue with Black Interior.


Joined: 4/1/2007
Posts: 432

I have the original Q-Jet on my 72 454. Been rebuilt and seems fine. My question, is the vacume at the top front passenger side of the carb the same as manifold vacume or is this location on Q-jets considered ported vacume?
thanks 
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Carb Vacume Question (2/15)
 5/20/08 9:58pm
KOPBET
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Tulsa, OK - USA

Vette(s):
1973 LS4 4 speed Coupe. Silver & Oxblood 1996 LT1 Coupe. Arctic White & Tan.


Joined: 4/26/2007
Posts: 152

Top front passenger side is full manifold vacuum for the choke pull-off.
 
Hey Okie, are you going to the Vette show in Norman next month?
Carb Vacume Question (3/15)
 5/21/08 9:12am
bio11
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Oklahoma City, OK - USA

Vette(s):
1972 LS5 Convertible,Auto.Targa Blue with Black Interior.


Joined: 4/1/2007
Posts: 432

When and where is it? I would like to go but it will just be to look since mine is not done yet. I'm still working on the interior. Notice only one seat in the picture. Thanks for the reply, that outlet on my carb is were my vacume advance is currently connected. According to all my books that looks like the correct location.
Thanks
Lonnie
P.S. are you going to have yours there? if so I'll look ya up.
Carb Vacume Question (4/15)
 5/21/08 12:40pm
KOPBET
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Tulsa, OK - USA

Vette(s):
1973 LS4 4 speed Coupe. Silver & Oxblood 1996 LT1 Coupe. Arctic White & Tan.


Joined: 4/26/2007
Posts: 152

June 6th and 7th at the Riverwind Casino. I plan to go down that Saturday morning, pick up my son in Moore, and just go see the cars and network a little bit. I don't plan on participating in the judging event, so I probably won't drive the shark because of that. But I will be in the C4.
 
 
Your post indicated "top front passenger side". You should have a vacuum dashpot there to operate the choke pull-off linkage. Where is it plugged in now?  
 
 
 
Carb Vacume Question (5/15)
 5/21/08 11:11pm
bio11
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Oklahoma City, OK - USA

Vette(s):
1972 LS5 Convertible,Auto.Targa Blue with Black Interior.


Joined: 4/1/2007
Posts: 432

The chock pull-off comes of just below the one on the top corner about a 1/2 inch and it is angled toword the vacume pot. It was connected when I got it back from being rebuilt. The carb guy said the top corner was for the vacume advance. It has a tube coming from the distributor and when it gets to the front of the carb it curves up and connects with a piece of hose about 3 inches long. I've read about wanting manifold vacume for your advance and wondered if this was or not.
Carb Vacume Question (6/15)
 5/21/08 11:51pm
KOPBET
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Tulsa, OK - USA

Vette(s):
1973 LS4 4 speed Coupe. Silver & Oxblood 1996 LT1 Coupe. Arctic White & Tan.


Joined: 4/26/2007
Posts: 152

So do you have an automatic?

Carb Vacume Question (7/15)
 5/22/08 11:36am
bio11
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Oklahoma City, OK - USA

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1972 LS5 Convertible,Auto.Targa Blue with Black Interior.


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Yes it is an automatic, I did notice on Q-jet numbers the last # is even or odd for auto or 4speed. It does have the correct # for auto. My modulator vac comes off a tee on the manifold between the distributor and the carb. Passenger side to modulator and driver side to vacume canister and accessories.
Carb Vacume Question (8/15)
 5/22/08 10:08pm
KOPBET
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Tulsa, OK - USA

Vette(s):
1973 LS4 4 speed Coupe. Silver & Oxblood 1996 LT1 Coupe. Arctic White & Tan.


Joined: 4/26/2007
Posts: 152

Does your carb should look like (similar) this?
 
 
KOPBET2008-05-22 19:09:09
Carb Vacume Question (9/15)
 5/23/08 8:45am
bio11
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Oklahoma City, OK - USA

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Mine has a straight tube coming out above the one for the choke pull-off. other than that it looks the same.
Carb Vacume Question (10/15)
 5/23/08 12:59pm
KOPBET
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Tulsa, OK - USA

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1973 LS4 4 speed Coupe. Silver & Oxblood 1996 LT1 Coupe. Arctic White & Tan.


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Can you post the numbers on the carb or pics?
Carb Vacume Question (11/15)
 5/24/08 11:22am
bio11
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Oklahoma City, OK - USA

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1972 LS5 Convertible,Auto.Targa Blue with Black Interior.


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I'm not good with pics but the # is 7042208. according to my ID info is as follows,
70=Rochester ID
42=1972
2 =49 states 5=california
0 or a 1 or 2 = Chevy
8=auto    even# = auto odd # = manuel trans
I called the carb shop that rebuilt it and he said that top tube was for the vac advance but he didnt know if it was full intake vacume or not. He said he thought it was after it had reached operating temp and chock had pulled off. So I guess I'll leave my vacume advance hooked up to it for now.
Carb Vacume Question (12/15)
 5/24/08 12:08pm
rraider1
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Woodland, WA - USA

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1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion


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Here is a good carb info site http://www.carburetion.com Yet another info site
Carb Vacume Question (13/15)
 5/24/08 12:20pm
rraider1
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Woodland, WA - USA

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1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion


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Your Carb number  goes to 1972 GM truck G10/20 and 30 series 350 all trans if the site number check is correct
Carb Vacume Question (14/15)
 5/24/08 1:14pm
KOPBET
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Tulsa, OK - USA

Vette(s):
1973 LS4 4 speed Coupe. Silver & Oxblood 1996 LT1 Coupe. Arctic White & Tan.


Joined: 4/26/2007
Posts: 152

That's what I was afraid of. That is not your original carb. If you had an original carb before you took it to the shop it appears they pulled a fast one on you.
 
 
You can get a vacuum gauge and hook it to where the choke pull-off is hooked up, and if you see full manifold vacuum all the time then that is where it goes.
 
The vacuum advance location described to you can be checked the same way. If there is little or no vacuum at idle then that is a ported location and is a suitable location depending on your engine configuration.
KOPBET2008-05-24 10:34:28
Carb Vacume Question (15/15)
 5/24/08 6:32pm
bio11
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Oklahoma City, OK - USA

Vette(s):
1972 LS5 Convertible,Auto.Targa Blue with Black Interior.


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Posts: 432

my AIM book shows this carb for the LS5 big block with the advance coming off just like it is. But now I'm wondering if it has the wrong metering rods and stuff in it. I guess I'll do some inquiring next week with the local carb guys. I looked at the site rraider1 had and he's correct. Since it showes truck 350 it may be the same carb just metered differantly. First I'll chew out the guy that rebuilt it for not telling me.
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