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Old 06-22-2016, 09:47 PM   #1
dmjlambert
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Stock vacuum setup for 350 CI engine and Quadrajet?

Does anybody have a stock setup for their 350 CI engine with TH400 transmission and Quadrajet with divorced choke? I would like to know what the proper vacuum ports are to use for each component so I can return to stock as reasonably close as possible. I have a 1969 CST/10. The only upgrades I have going on is HEI distributor, and I have a Quadrajet with electric choke on order to replace my Quadrajet with divorced choke. Can you tell me if my guesses are right about the connections and fill in the missing pieces?

1. It looks to me like there is a long tube sticking out of the carb pointing to the passenger side of the truck, behind the vacuum break, and the heat riser snorkel diverter old stiff and cracked vacuum line that is attached to the air cleaner looks like it could have been connected there. If so, I will plug that because I don't have a working heat diverter now.

2. I see a large port under the fuel intake, the PCV valve connection.

3. I have another small port on the front driver's side of the carb. I'm thinking that should go to the distributor.

4. There is a very short hose running from the front passenger side to the vacuum brake, so I'm thinking that is correctly hooked up.

I don't see any other ports on the carb. I don't know if my new Quadrajet with electric choke will have the port behind the vacuum break.

5. Behind the carb on the manifold I have a hex-shaped tube sticking up with 2 ports on it. One port points straight to the passenger side of the truck, and one points toward the passenger headlight.

I have factory A/C and there is a vacuum canister that I won't hook up at this time, but would like to know the proper port for it and will plug the port. The vacuum canister is only for A/C and heat diverters and controls, is that right? Those are a mangled mess for another time.

The transmission has a steel vacuum line coming up from behind the engine, and I don't know what exactly that needs vacuum for, or which port to use for it.

On a semi-related note: I have the wires coming from the transmission and through the firewall from the fuse panel that would go to somewhere in the vicinity of the carb (I think) for the wide open throttle switch for transmission kick down. The problem is, I have never seen what this switch looks like or where it may be. Perhaps attached to the carb or on the throttle linkage somehow, but I think it may be completely missing from my truck. I would like to know what a stock wide open throttle switch looks like and how it is connected, if anybody has a stock truck with the TH400 transmission and Quadrajet. I was not able to find anything decent online, except some weird looking aftermarket switches and under-the-gas-pedal setups. I have seen them referred to as WOT switches, and they appear more common to disable A/C clutches than for transmission kick down. Perhaps the one on this truck did both functions, but in 1969 I'm guessing it did just the transmission kick down. I don't know if the linkages will look the same on my new carb, but I'll see when it arrives.
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Old 06-22-2016, 10:30 PM   #2
Wrenchbender Ret
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Re: Stock vacuum setup for 350 CI engine and Quadrajet?

1-4 you are correct. #5 this port is used for the trans modulator & the A/C controls. If it has a large dia. outlet like 3/8 or5/16 it is for power brakes.
There was a kickdown switch by the throttle arm & linkage. I don't have a photo though.
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