Mystery vacuum lines🤔

[Pghcc2006]

Good evening gentlemen,

Does anybody know what the vacuum line with the screw in it and the black plastic one that seems to be coming from the distributor is for?

I have the service manual but I'm still stumped.

[fishnjim]

Can't exactly tell and no year/engine, but the silver "thing" coming out the rubber nipple on the valve cover is the PCV.   So those teed off tubes are connected to either the carb, air cleaner, or manifold.   
The one you say comes from the dist is likely the vacuum advance, but the hose looks a little too large for that?   Looks like somethings missing with the half engaged bolt in the manifold so maybe some connection or device went there.  Look in the smog control part of the manual.
Some PO has done some "surgery" on this motor.  Lots of "jabberwonky" thinking during the smog control era.  Things were changing rapidly and many attempts to overcome the low compression to extend gas mileage.  I've never figured out how they justified poorer mileage and cleaner burning.  But they had to meet the EPA rules, nontheless.

[TJ Hopland]

Its a 75+ is about all I can tell.  The hose plugged with the bolt seems a little to large for that area since it doesn't look like its in that PCV line but maybe we just can't see it properly or its totally in the wrong place or maybe its slid over a smaller hose? 2 wrongs make a right?

If you have the service manual you should be able to start tracing things and take note of what is correct.  Do something like mark what is correct with a piece of painter tape so you know not to worry about things that are marked.  That should make it easier to figure out whats left.   You can also make a copy of the vacuum diagram and mark off the lines on the diagram as you confirm them.  Should be easy at that point to look at what isn't marked and figure out what is wrong or missing.

These mid to late 70's are not that bad line and wire wise, the 80's were much worse especially if you were not GM.  80's you can't hardly see the engines under all the wire and hoses.

[Pghcc2006]

Car is a Canadian market 1976 Fleetwood with the 500 BTW

[V63]

The Canadian market at that time had US federal emissions as I had a 74 fleetwood with same. Someone probably disabled the ported vacuum switch would be my guess but it is important the distributor vacuum advance has a vacuum supply and that the chamber actually functions.

If the automatic level compressor is not functioning (probable) i would eliminate its vacuum supply supply as a probable leak affecting engine performance. It's the larger T in your images.

[TJ Hopland]

I was wondering if Canada did anything different but if it was just the US Fed version the manual should be accurate as to how it was originally.

What does a 76 have on the charcoal canister? Did that have active controls so like 5 lines or was it still the basic version with just 2 or 3?   

[Big Fins]

Not to be a smart azz, but the complete diagram is in the factory service manual at the back. Over the years and owners, many mods to the system were done in the way of making the car run smooth, instead of lean for emissions laws. Thermo vacuum valves were bypassed, ALC systems bypassed because the pumps quit and air diverter doors were bypassed. Even vacuum feeds to the A/C system were bypassed because parts were/are near impossible to find.

Unless you have an engine that is like new and all of these systems work properly, putting them back to factory specs and operating as intended is difficult to say the least.

[TJ Hopland]

Sure things could have been modified but a good starting point is to take the original diagram and figure out what you currently have.  What's missing and what is hooked up wrong vs just not hooked up. 

[hirvine]

On my '72 Eldorado, a line that was teed like that (and was that size) went to the smog pump (per the attached drawing, which was not 100% accurate for my car).

A smaller line went from the carb to a thermal vacuum switch at the front of the engine.

As others have said, the bigger teed line from PVC goes to the rear suspension level compressor.

I gave up on all of this stuff and deleted it all - but I had fun figuring it out before I did so.