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

[JeffBowlsby]

That's pretty good advice but a couple of clarifications:

The two port throttle body is a 73 2.0L version, the 74 only has a single port - nothing to cap off on the 74 version.

It is better to keep the decel valve in place because it functions as a vacuum signal buffer to the MPS and offers no performance gain in taking it out. Removing it puts increased strain on the MPS diaphragm which is critical to the FI system.

[brant]

That's pretty good advice but a couple of clarifications:

The two port throttle body is a 73 2.0L version, the 74 only has a single port - nothing to cap off on the 74 version.

It is better to keep the decel valve in place because it functions as a vacuum signal buffer to the MPS and offers no performance gain in taking it out. Removing it puts increased strain on the MPS diaphragm which is critical to the FI system.

Jeff
I absolutely agree with you regarding keeping the decal valve in place on a FI car
I agree with your point about bleeding off excessive vacuum signal that could damage the MPS

and I am theorizing a 2nd reason for keeping the Decel valve in place:
that being that the excessive vacuum signal on decal, can cause the diaphragm to flex excessively, and would also change the mixture excessively. So the opening of the decal valve keeps the mixture closer to the max vacuum signal mixture that is programed into the stock settings.

1)protecting the diaphragm
2)limiting the mixture change on decal or high vacuum settings


these german engineers think of everything
brant

[poorsche914]

Have you taken a look at pbanders D-jet page?

Tons of information and should help you sort out what parts work best together.

(IMG:style_emoticons/default/driving.gif)