engine and drivetrain 72 Vacuum Questions

[Dake]

I'm very new to the vacuum system on cars in general. The PO removed nearly all of it, and it's a 72 so it had little in the way of valves etc. to begin with.  The car currently starts but then stalls and refuses to start again, and while I doubt any of this stuff will solve that, it's a step.

 

Question 1. I have a Pertronix Ignitor electronic distributor, so does that define whether or not I need vacuum advance or retard coming from the distributor? I read some topics where distributor advance was necessary and some where retard was necessary, and some where neither were hooked up.

 

Question 2. What vacuum lines will I be left with? I've read conflicting topics: some people plug all of the manifold holes and the brake vacuum assist system, while others connect some lines and plug others. I have circled and numbered some holes in the manifold, and my header shroud is long gone. Some of these holes might have nothing to do with vacuum; as stated, I'm a noob right now.

 

I'm a very visual person, so if someone could identify the circled items and their purpose, such as where the line should end, and importantly which are necessary and which can just be plugged.

1. Open hole

2. Open hole

3. Open hole

4. Has an open threaded hole at the bottom

5. Has a braided hose coming from it, but it's capped at the end.

6. Open hole. I've seen some people stick an air filter here.

7. Open hole.

 

8. Not pictured, but there's no line going to my brake booster for vacuum assist. I've read that line is not explicitly necessary but braking will be heavier. Where does it source from?

 

The only line to or from the carb is the fuel-in line, besides the water lines. It's a Weber 32/36.

 

Thanks everyone!

Edited January 16, 2014 by Dake

[Mike87]

The line from #5 goes to the brake booster.

 

Make sure that #4 is closed so that nothing gets into the intake manifold. There really is no reason that there should be a valve in that area. Plug that hole and leave it alone.

 

Pertronics ignitor is just the trigger in your distributor.(it is a replacement for the original points that were in there) Your distributor should have a canister on the side of it with a nipple on it. Connect a vacuum line from that nipple to the nipple at the base of the carb. That canister will be your vacuum advance.

 

#1, 2, 3, and 7 are not used and can be left alone (assuming #1 is just a mounting hole) If #1 is a hole that goes into the manifold, plug it.

 

#6 is your breather. In a perfect world, it should be connected to the air cleaner so the engine burns the vent gasses. Some people leave it open, others connect it to the air cleaner, others put a small filter on it.

 

You might consider doing a search on this site for more information. There is a lot of it here.

Edited January 16, 2014 by Mike87

[Dake]

Thanks for the info there. I fould a lot of incomplete or unclear topics, and I know my car's been messed with and isn't perfectly stock. I don't seem to have a solenoid for vacuum advance on the distributor, so I plugged the port on the carb and it does start and run with some carb fiddling. Is vacuum advance a necessary thing or is it possible to run with neither advance or retard?

[Mike87]

It has been my experience that the vacuum advance works better on a standard engine, especially in the low to mid rev range. Typically the centrifugal advance of the tii distributor (the one you have) is better suited for the tii (or fuel injected/dual carb/high compression) engines due to its smaller advance duration. You should be able to tune your engine with that distributor to make it run OK.

 

BTW, you still have advance in your distributor, it is all centrifugal and no vacuum. The other type of distributor has both centrifugal and vacuum (advance and/or retard).

[Dake]

Thanks Mike, that's all very helpful in understanding the mechanics at play here.

 

I will tackle the unlit propane torch test at some point, but as of right now I've plugged 1, 4, 5, routed 6 to the air filter box, plugged the pictured yellow cap on the manifold, and capped both of the ports on the Weber 32/36, and the inlet on the brake booster. I feel like now there's no vacuum system at all, and I don't feel like that's correct. It was only started for a few seconds at a shop today before someone asserted it had a vacuum leak somewhere, so I guess the next step is checking gaskets and seals with the torch.

[Dake]

The car will idle fine but as soon as I drive it anywhere, when I take it out of gear the revs shoot sky high. No amount of carb tinkering seems to fix this, but as per the pictures above I feel like I've dealt with every vacuum source. Is there any other reason that would happen besides a mystery vacuum leak?

[Mike87]

You may have a large vacuum leak, but not too large. If it gets too big then the engine will not run. I would look at your choke mechanism. It may be holding the throttle open.