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

[Olympic 914]

Does your distributor have one or two vacuum ports ?

I have two ports on the distributor. The distributor is one of the original 73 1.7 parts.

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

I am using the 73 1.7 ECU (#037) and that was also used on the 73 2.0 .

I do have a variable POT that I will be using to determine the value needed for the ballast resistor inline from the CHT sensor.

Also I have a 043 MPS that was rebuilt and set to the 037 MPS specs that were used on the 73 2.0

I have tried to stay pretty true to the 73 2.0 FI setup, but I have made other changes to the engine, taking it to 2056, using HAM RS+ heads and a Raby 9590 cam.

I understand these changes may require a little fine tuning of the MPS and fuel pressure to get it to run correctly. I will be adding a Autometer Wideband AFR gauge to help in the tuning.

If both vacuum hoses were connected on the 73 2.0 setup I may just leave them hooked up. unless there is a negative effect to leaving the retard side connected.

[JamesM]

I am using the 73 1.7 ECU (#037) and that was also used on the 73 2.0 .

I do have a variable POT that I will be using to determine the value needed for the ballast resistor inline from the CHT sensor.

Also I have a 043 MPS that was rebuilt and set to the 037 MPS specs that were used on the 73 2.0

I have tried to stay pretty true to the 73 2.0 FI setup, but I have made other changes to the engine, taking it to 2056, using HAM RS+ heads and a Raby 9590 cam.

So, its more than just an inline resistor that makes the 1.7 ECU work with the early 73 2.0s, the head temp sensor itself was also unique to that application. You can futz with all the variable resistance you like to get it running good when fully warm but the entire resistance curve is different so warm up mixture is always going to be an issue unless you can find a 0 280 130 017 sensor. These days though it might be easier to just find a 74 or 75 ECU.