So I'm in the process of installing a new engine in my 75, and I'm having a bit of trouble figuring out how to connect all the vacuum hoses to my new Quick Fuel HR-680-VS carb (holley style).

So the carb has four ports for vacuum:

1. Port specifically for the PCV
2. "Full Manifold Vacuum" port
3. Timed spark port on the lower front
4. Timed spark port on the back

Here's what I know has vacuum hose to connect:

1. PCV
2. Distributor
3. Brake Booster
4. Headlight/Accessories (used to include A/C system)
5. Vapor Canister

So the PCV is simple enough and distributor goes to one of the two "timed spark" ports, but about the rest? The brake booster was originally connected by itself to a port on the old q-jet carb. I've read that the vapor canister can be combined with the PCV, but that doesn't seem right to me. The headlights and stuff were originally connected to a fitting on the intake manifold.

I was considering connecting the brake booster and vapor canister to the fitting on the intake manifold and then connecting the headlights to the "full manifold vacuum" port on the carb. I sent an email to Quick Fuel to see what their thoughts were, but they didn't really give much information back.

Any advice would be greatly appreciated... I'm holding off buying hoses and fittings/clamps until I get this figured out.

 

Doesnt the intake manifold have any potential ports or plugs that could be turned into ports for the brake booster and accessories? The PCV and Vapor Canister should be connected with a T fitting, factory did it on certain years. The brake booster should not be combined with either the PCV or vapor which is stated in the instructions that came with the carb.

 

Yeah, there's a port on the intake manifold for vacuum... That's where I was planning to connect the brake booster.

 

so connect the booster and the accessories to the manifold port

 

Is your car a automatic? If it is and TH400 you will need one for the modulator.

 

I'm swapping the TH400 for a TH200-4R from BTO with their TV kit. I checked my documentation but didn't find anything about connecting a vacuum line on it. It has an electrical connection on it, so I assume that is taking place of the vacuum line... Feel free to correct me if I'm wrong about that.

 

So there's nothing special about the brake booster connection that made it have it's own connection on the q-jet? I didn't think there was, but after looking at the old setup, it had me wondering.

 

Vacuum for power brakes should come from a dedicated connection at the base of the carburetor. Nothing should share the line with the booster.

AT and vacuum accessories should come off an intake manifold fitting on a runner at the rear of the manifold between the carb and the distributor.

 

The PCV valve outlet hose needs to be connected to a larger port at the base of the carburetor (usually the front); one of the smaller manifold vacuum ports is not really large enough to get adequate flow from the PCV valve.

The main vacuum supply line needs to be connected to manifold vacuum...either directly from the intake manifold or from a manifold vacuum port on the carb. It should NOT be connected to the same port as the PCV hose. There should also be a line filter and check valve placed in that line, and it should run to the inlet connection on the vacuum reservoir tank (either a side tank in the left fender or a 'pipe' tank in the front end of later '70s cars). The headlight/acc. feed line should then be "T"-ed into the main feed line [after the filter/check valve] or connected to an outlet fitting on the side vacuum tank.

Distributor should be connected to manifold vacuum port on carb. Originally, it was connected to a 'ported' vacuum fitting on the carb, but that is for emissions purposes only...the engine "prefers" it to be connected directly to manifold vacuum.

The vacuum canister "purge" line can be "T"-ed into the PCV hose going to [or at] the carb base fitting. The vacuum canister "signal" line should go to a 'ported' vacuum fitting on the carb (so that the canister does not purge during idle condition).

The brake booster normally is fed from a large port on the back side of the carb base; but, it can also be connected directly to a 1/4" pipe connector at the intake manifold.

Hope that helps.

 

Wow! This has all been extremely helpful!

The car isn't equipped with a vacuum canister, just the vapor canister in front of the fuses on the driver's side and below the washer tank. I was actually considering adding one because the new engine will have less vacuum. Any thoughts on those? Good enough or are the electric pumps a better (more expensive) option?

 

Headlights always have a vacuum reserve tank. See if you don't have fittings on the front crossmember. If you do not use a reserve tank, the engine will have to be running in order to open and close the headlight doors any time you want to do maintenance on the lights. Not killer, but a nuisance.

 

OH!!!!

Thank you for clarifying that! I couldn't figure out why the headlights connected up to what looked like part of the frame...

I'd really like to convert to McSpeed Killer headlights, but that's not in the cards right now...

 

One more question...

Does anyone know the fitting size for the vacuum port on the intake manifold? I think it's 3/8" NPT, but I just want to make sure.

 

I would be surprised if that fitting was any larger than a 1/4" NPTF fitting.

 

I ordered a nickel plated brass 1/4" NPT fitting (wanted it to look nice), turns out the vacuum port is definitely 3/8" NPT. Probably should mention the intake is a Dart Air Gap in case port size changes with different intakes, but I wouldn't imagine that's the case.

I had previously ordered a 3/4" NPT fitting for a port that measured 3/4" (the manufacturer website said it was a 3/4" port) and that was wrong. A 3/4" NPT fitting is 1" OD, so what the manufacturer meant was OD on their specs but didn't list it. This time around I should have known the conversion factor when I ordered this fitting.

Anyway, the day I ordered the part I either measured really bad or my math skills were off cause the vacuum port measures 5/8" OD which is 3/8" NPT. The 1/4" NPT fitting I ordered measures 1/2" OD. Yep... Dumb move...