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

[mgphoto]

Good looking job, you will have some issues mixing and matching, dizzys, mps's and ecu's.
The ecu will determine how the vaccum lines are used.
One of the hoses is the vacuum retard and the other vacuum advance, that is the reason one of the nipples is above the diaphram and the other below.
Off the top of my head, I believe the 1.7 ecu is used with the 2.0l 73 FI, which requires the ballast resistor on the head temp sensor.
The 74 2.0l FI deletes the resistor and the vaccum retard, they cap the throttle body and leave the vacuum can unplugged.

'74 ecu and dizzy "vacuum can" are tuned. If you don't have the 2.0l dizzy your vaccum signature will not match the vaccum can response. You can either use a 2.0l dizzy or find a vaccum can that has a slotted screw with a locknut in the middle of the can, these can be adjusted to match the vacuum signature.

You will also need to turn the mps using an air / fuel ratio meter if you've increased the engine capacity.

Unless you have a concorse need, I would remove the deacceleration valve and cap the port on the plenum.
Just my 2 cents.
Good luck,
Mike