So I am currently finishing up my 71-72 350 rebuild I have to Quadrajets 17058213 ( a 77 or 78 i believe) and a 7041211 ( a 71 0r 72 I believe) I have already rebuild the 7041211, but am now realizing that that one has different vacuum ports, especially the one on the back bottom center is missing, which I believe is for power steering. Is it going to be possible to use this older one and hook up reliable vacuum for power steering and power brakes, or should I just rebuild the other new one? Thanks for your help
I essentially need help making a vacuum map for pcv, brakes, and steering and fuel , ect does the vacuum for brakes / steering come off carb or intake manifold?
Spencer, you shouldn't need vacuum for power steering but for your power brakes you can use vacuum from the rear carb port or the intake itself. The brake booster will be indifferent to the source as long as you're getting manifold vacuum. You likely have a tapped hole in an intake runner behind the carb on the intake manifold. It's probably a 3/8 NPT pipe thread. You can use a regular hose barb fitting with the proper hose diameter as a vacuum source if your quadrajet doesn't have one. I highly recommend Cliff Ruggles' book on Quadrajets, it is very helpful and an invaluable resource, well worth the money. There should be a 3/8 inch hose barb on the front of the carb on the baseplate that is used for the PCV. There are benefits and drawbacks to each Quadrajet, the book goes into detail on this and also offers many tips and tricks that can be utilized on the street for improved driveability, performance, and fuel economy as well as on the drag strip.
Spencer, This should help you. See the following 2 pictures As 'Indestrutableforce' has said, I too would suggest picking up the vacuum source from the intake manifold to go to the power brake booster.
AHOTROD - Great Pics INDESTRUCTABLEFORCE - Thanks for all the info, I will definitely look into that book it sounds like a must have if I am going to continue working with quadrajets BUDGET36 - I got confused translating form my gm diesel thoughts, on a gm diesel power steering and Brakes are connected because there is no vacuum. Thanks so much its a crunch to get this motor built
So Power steering needs no vacuum Power breaks can come of the port on manifold, which already has a twin barb (1/8th in) but I will probably need to upgrade that to 3/8 because the carb i rebuild does not have the rear port There is an additional port on front of manifold that is 3/8 with a barb on it, that must be hot water for heat? Pcv - port is on the old carb so we are set there
The port on the front of the intake manifold is for the heater. Hose size for it is 5/8". Yeah, for the brake booster fitting you'll need a fitting for a 3/8" hose.
A pic is worth 1,000 words.......PCV port can be used for the power brakes. Almost all of teh SBC intake s have a vacuum port in the #8 inteake runner behind the carburetor for the power brakes and transmission modulator and vacuum advance and a/c system vacuum source.....
@AHotRod , while you're educating us lesser mortals, mine also lacks the port labeled "to dist advance" and my advance is hooked up to the port above it you labeled "cap off". The port you suggested in post #12 to @Spencer313 is capped on my carb. Does it matter? Car currently isn't drivable so I don't know if I have an issue. Thanks for taking the time to share your knowledge.
Bread, Without a good photo of the front of YOUR carb all I can tell you is that you need base-plate vacuum. Is your carb like the one in latest picture? Glenn
Thanks again, I was thinking that one, but the guy had it capped off, who knows why.... form the looks of the insides of the motor it had been running like garbage for a while
@AHotRod , here are pics of my carb. The port for the PVC is blocked cuz the motor came to me without a PVC. I'll be adding one. You can see the upper passenger-side port routed to the vacuum advance and the driver-side port blocked off. There isn't a lower pass-side port.
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