D-Jet vacuum hose question, Which hose, or Both? Options

[Olympic 914]

Just finished up installing all the FI wiring harness and the vacuum hoses and now the engine compartment looks like a bowl of Spaghetti.

This engine started out as a 73 1.7 with the stock FI and I converted everything to a 2.0 system. I did use some of the original 1.7 parts as they were the same for both engines. But all the 2.0 FI parts ( throttle body, plenum, air filter housing ,etc.) where cobbled together from fleabay purchases and I am not sure what years those parts were from. Also used the original 73 1.7 FI wiring harness and ECU and had to make a couple extensions to get everything to hook up. Not much problem there, (except for trying to connect those ground wires under the plenum. )

Now to the question, I was using Bowlsby's vacuum diagram that is for a late 74 2.0 system and while hooking up the vacuum lines to the dizzy it seem that one line is no longer used.



in the diagram above I have the green vacuum hose connected from the throttle body to the dizzy as shown by the Orange circles. I also have another vacuum port on my dizzy that I have connected to the second vacuum port on my throttle body shown by Blue circles.

Should I have both of these hooked up? or do I disconnect the Black vacuum line as shown in Bowlsby's diagram and just plug the second port on the throttle body.
This is what I have hooked up now.



Is there a reason that the later versions did not have this second port hooked up?
What benefits are there to using the second line to the dizzy vacuum canister?

in picture below the green line from the throttle body is routed differently

[GregAmy]

Camping a relevant question onto this discussion thread...

'74 2L; no idea if it's early or late, but not germane to the question. When I got the car it wasn't running, hoses removed, ports capped off. AAR and decel valve not installed.

I'm slowly reinstalling equipment, and the decel valve is next. Fortunately I found one in the Box 'o Parts and it works, though I had to adjust it WAY out to get it to move at the 17 inHg that Anders suggests. It appears I need to get some 10mm hose, and I see that there's 10mm ports on the airbox and plenum (both of which are plugged now), so I'm good there.

However, in the Post #1 drawing the decel valve vac control line appears to go to a fitting on the right front of the plenum, and the diagram shows some kind of tee fitting there. I don't have that on my car, it's also plugged off. Does anyone know the size of that plenum fitting, and if that tee is required? Can I tee into the distributor vac line to control the decel valve?

For reference, on my car the PCV hose off the oil fill is going directly into the airbox, where the AAR goes into in the drawing. Is that correct? Do we allow the to pull air directly from the crankcase ventilation into the intake plenum? Isn't that a very big vacuum leak?

Finally, my distributor may be routed incorrectly. The inside vac line (orange circle in the drawing in Post #1) is going to one of the vac fittings on the throttle body, but the outside vac line (blue circles) is going to a vac line fitting on the opposite side of the throttle body. I can't tell in the drawing where the blue-circle line is supposed to go on the plenum?

So, TL;DR:

- What is that tee fitting where PCV and decel valve vac line go to, and if it's needed where do I get one?
- Is the fitting on the plenum where that tee goes into 10mm? Can I just go directly to that?
- Can I tee off the distributor vac line to control the decel valve?
- Where does the outer side of the distributor vac canister go to on the plenum?

Edit: to add to my grief...I just pulled the plug off the 10mm port on the plenum, and someone had trimmed the length! It's only about 1/4" long now, which explains why it was being held on with a hose clamp. Dammit, why do people do stuff like that???