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Author Topic: Vacuum line routing/connections for carb and air cleaner help needed (Pics)  (Read 6542 times)
NotplayN
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"So many cars, so little time"


« on: May 15, 2011, 09:06:07 PM »

Hello all,

Where do you connect the vacuum lines that come off vacuum switch on the air cleaner?


Also if someone could look over the other pics and tell me if you see something wrong with the routing



Thanks
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1979 Trans Am 400 4spd matching #s
1997 Firehawk LT4 #3 of 29
2003 Cobra Convertible
1987 Buick Grand National SOLD
2008 F350 Duelly Tuned
2010 Shelby GT500
Grand73Am
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« Reply #1 on: May 15, 2011, 09:33:04 PM »

Outside line goes to the vacuum tree behind the carb, and the line closest to the air cleaner goes to the rear vacuum break on the carb.
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Steve F.
NotplayN
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"So many cars, so little time"


« Reply #2 on: May 16, 2011, 06:51:43 AM »

Here is a pic of the back of the carb. Where would the vacuum tree be located? and the vacuum brake?
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1979 Trans Am 400 4spd matching #s
1997 Firehawk LT4 #3 of 29
2003 Cobra Convertible
1987 Buick Grand National SOLD
2008 F350 Duelly Tuned
2010 Shelby GT500
ILLTA77
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« Reply #3 on: May 16, 2011, 07:47:21 AM »

The vacuum tee goes in the back of the carb, where you have the brass fitting for the brake booster.

« Last Edit: May 16, 2011, 01:30:26 PM by ILLTA77 » Logged
Grand73Am
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« Reply #4 on: May 16, 2011, 11:06:18 AM »

The rear vacuum break is that gold vacuum can behind your choke housing on the carb.

Here's a closer picture of the vacuum tree that's normally on the back of a Pontiac q-jet, and another one on another engine(not mine). You can see the pipe on the vac tree that could be used in this pic:



« Last Edit: May 16, 2011, 11:12:37 AM by Grand73Am » Logged

Steve F.
NotplayN
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Posts: 364


"So many cars, so little time"


« Reply #5 on: May 16, 2011, 04:15:44 PM »




So #1 is the vacuum brake, so I need to connect it to #4, right now that is attached to A. what should be attached to A

#5 and #6 are connected to B and C??.......... can I connect the end of #6 to the empty spot on the carb created by moving #4 to the vac brake?

 Thanks
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1979 Trans Am 400 4spd matching #s
1997 Firehawk LT4 #3 of 29
2003 Cobra Convertible
1987 Buick Grand National SOLD
2008 F350 Duelly Tuned
2010 Shelby GT500
TripleTransAm
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Posts: 1769



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« Reply #6 on: May 16, 2011, 04:53:05 PM »

One of those... possibly A... should have been connected to the air intake tube for the choke heater, which I just now noticed you are not using. I seem to recall on both my L78 and W72 that the *other* loose vacuum hose would plug somewhere in the front of the carb to a small port. It's still vivid in my mind because that hose was somewhat brittle on my W72 and the end actually broke off at the carb as I went to pull on it, so I cut a fresh length and replaced the whole line.

(I'm thinking it's the port above the driver's side idle mixture screw but I can't really recall for sure. Is that a factory Qjet, by the way? I ask because I just noticed the edelbrock logo on the manifold, so....)
« Last Edit: May 16, 2011, 04:54:59 PM by TripleTransAm » Logged

/Steve
1987 Trans Am GTA
1998 Trans Am WS6
1978 Trans Am L78 (sold)
1978 Trans Am W72 4-speed WS6
TripleTransAm
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« Reply #7 on: May 16, 2011, 04:59:21 PM »

Here's a pic of my L78 carb (xxx276) from 11 years back, way before I cleaned it up and rebuilt.



Willing to bet the port I'm referring to is the shiny one visible above the fuel filter housing. I know the carbs are different for W72 but to the point of different casings? Also, it looks to be oriented in the same way I remember pulling when it came to my W72.
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/Steve
1987 Trans Am GTA
1998 Trans Am WS6
1978 Trans Am L78 (sold)
1978 Trans Am W72 4-speed WS6
TripleTransAm
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Posts: 1769



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« Reply #8 on: May 16, 2011, 05:09:51 PM »



Here it is in 2008, all buttoned up and cleaned up. Definitely the port I'm referring to is the one next to the filter housing (unplugged here), so in your case it's definitely going somewhere up front.  (evap canister?)

Funny thing is that I see 2 members here (original poster included) that show the same routing for that port which differ from both my 400s which show the same routing to each other. I could have sworn my emissions labels on both cars corresponded with how the cars were set up.

Which leads me to a further thought: all this info can be gleamed off the emissions label on the rad support!
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/Steve
1987 Trans Am GTA
1998 Trans Am WS6
1978 Trans Am L78 (sold)
1978 Trans Am W72 4-speed WS6
TripleTransAm
Oracle Forum Member
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Posts: 1769



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« Reply #9 on: May 16, 2011, 05:15:17 PM »

PS: don't use my photos of my L78 as reference for routing of other emissions hoses, it's a high mileage (110000 miles) example that's lived a long and storied life. My W72, on the other hand, seems like a time warp but unfortunately, I've not yet had a chance to photograph the engine much.

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/Steve
1987 Trans Am GTA
1998 Trans Am WS6
1978 Trans Am L78 (sold)
1978 Trans Am W72 4-speed WS6
TripleTransAm
Oracle Forum Member
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Posts: 1769



WWW
« Reply #10 on: May 17, 2011, 09:51:21 AM »

Well, it's been bugging me for a day now, I've been searching the internet for vacuum hose routing info and found the following:



Clearly, the vac switch on the side of the air cleaner base seems to handle distributing vac from the tree at the back of the carb to the secondary vacuum break. The little port I was referring to doesn't seem to be indicated in this diagram, so I'm still pretty certain that it's the one feeding the Thermac valve (via the temperature switch on the underside of the air cleaner base). Not sure where that line connected to that port on your carb is routed to, at the moment.
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/Steve
1987 Trans Am GTA
1998 Trans Am WS6
1978 Trans Am L78 (sold)
1978 Trans Am W72 4-speed WS6
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