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]

But in my setup I have the fuel line for the CSV coming off the tap on the 1-2 fuel rail.

Yup. CSV line comes off the left fuel rail. Right fuel rail has a little screw in it.

You drive it in freezing weather? The CSV isn't activated above ~32F/0C. I eventually removed mine entirely.

[Stratfink]

Getting ready for a throttle body rebuild and planning to use a spare core, but noted a difference in my spare relative to the part installed in my 75 2.0L.

My installed throttle body has 2 vacuum ports which I understand are for the vacuum advance and retard (I actually found the advance line loose at the distribution vac can).

I am looking to confirm that the best course of action is to retain the dual ported throttle body versus rebuilding the single port body and capping the retard line at the distributor. Pretty new to this so I appreciate the feedback to confirm.

Pics of my installed and spare bodies are below.

Installed on my ‘75 2.0L:


Spare throttle body:

[wonkipop]

@Stratfink i suspect this is a bit similar to the L jets.
D Jet experts like @JeffBowlsby will chime in - they know for sure.

74 49 state L Jet 1.8s had the dual port throttle body hooked up to both the vac advance and retard sides of dist. vac retard went to idle port on TB. vac advance went to port in front of throttle plate.

the vac retard dealt with emissions at idle basically. lowered NOX. but ran hotter at idle.
the advance gave fuel economy and cooler running at cruise. did nothing for emissions.

the 74 cali L Jet had single port throttle body (or one of the ports capped).
only the vac retard was hooked up to the throttle body. (to idle port).
this meant lowered NOX and idle and additional slightly retarded ignition timing at cruise.
lower NOX hotter running at cruise.

california had higher emission standards in 74 than 49 states.

in 75, the 49 state L Jet ran the 74 californnia set up.
and the california 1.8 hooked up the EGR to the port on throttle body in front of throttle plate. the calif set up gave lower NOX at idle via the ignition timing, the EGR restored fuel economy and cooler running at cruise despite the slightly retarded timing, which served to lower NOX.

i imagine its similar for the D Jets.
though i am not sure it was split between 49 states and california like it was for L jets.

the double vac can distributor and ignition timing played a large part in emissions control during those years.

there is a bit more detail in the 74 L Jet thread in the originality section of this website.
it took us a bit to work it all out for the L jets.

[hndyhrr]

The de acel valve adds air into the mixture reducing hydrocarbons, so the engines would pass US emissions, only 2.0l euros have the valve, none of the 1.7 or 1.8 have it.

This is incorrect. Most of the 1.7s, all US-spec 1.8s, as well as US-spec 2.0s, have decel valves. I believe the early 1.7s did not have them.

--DD

I have a 70,.17 fi, build date april 70. I have decel valve

[914sgofast2]

I have a 1970 1.7liter without the deceleration valve. The car has a December 1969 build date. Wonder when the factory added it during the early production run?

[JeffBowlsby]

Decel valve was added in 1972. Could be retrofitted to earlier cars.

[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.

[wonkipop]

pay attention
@hndyhrr
@914sgofast2
@JamesM
this is a very old thread, you are responding to the wrong person back in time.

@Stratfink is coming in on old thread and asking a very specific question about vac lines from the distributor to the throttle body on a D jet 2.0

@JeffBowlsby - you must know the answer to @Stratfink 's question.

i know enough from searching out the very same question in relation to L jet throttle bodies linked to distributors to know that there were 4 different throttle bodies, (theorectically) for the 74 and 75 L jets according to the PET. but those part numbers do not come up as stamps on the throttle bodies. they all just have the same number sequence cast in but not the variant letters that come after the 9 digit part number.

and i've seen the same thing goes for the D jet 2.0 throttle bodies.

they D jets have the same throttle body as far as i can tell for 73 and 74 if you look at the PET. but there are two different throttle bodies for 75 on. one for calif and one for 49 states. i suspect its to do with how you hook up the vac hoses from the distributor.
the question that @Stratfink is asking. is he not?

i don't know about D jets.

but if the same question was asked of me about L jets this would be my answer.
all the L jets can be turned into any of the variants by simply plugging or unplugging the hoses, but you do need to have both ports on the throttle body.
and they all had the retard hose from the distributor hooked up to the throttle body.
it was the advance hose that was either plugged in or not plugged in.

in the case of L jets, if someone said which was the best i would not hestitate to say the 74 49 state. with the vac hoses all hooked up.

why.
because the 74s ran the same ECU. all they did was unplug the hose on the californian cars to make them run at cruise retarded slightly and run hotter, purely for emissions.
it was a dumb as that.

D jet. i don't know about. but i would suspect it was similar?
but i could be way wrong because i really don't know much about D jet.

[JeffBowlsby]

I had answered this previously in this same thread:

"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"

The ignition advance was not connected to the throttle body on the 74-76 2.0L cars. From the factory, a short length of hose ran from the advance port and was routed under the air plenum not connectoed to anything, which is what my diagram depicts

[wonkipop]

I had answered this previously in this same thread:

"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"

The ignition advance was not connected to the throttle body on the 74-76 2.0L cars. From the factory, a short length of hose ran from the advance port and was routed under the air plenum not connectoed to anything, which is what my diagram depicts

good stuff mr. b

interesting the D jets were just like the L jets then.
makes sense.
(IMG:style_emoticons/default/beerchug.gif)

in that state with the retard hose only the distributor will retard the ignition whenever there is engine vacuum.
thats either with the throttle closed at idle or when the engine is part open throttle at cruise or deaccelerating with the throttle snapped shut.

when the advance hose is hooked up it can only affect the distributor when the throttle is open. you get engine vacuum at cruise that will operate that side of the can.
the total advance is a nett figure. vac can advance - vac can retard = total vac advance added to mechanical (centrifigal) advance.
thats the way it works. thats why the vac advance side of the can is larger than the retard side.

hence my view that the versions which utilise both sides of the can -
that would be a 73 2.0 (thanks mr. b) and a 74 49 states L jet - are probably better from a driveability fuel economy point of view. you would have to drive the two versions side by side to notice the difference and i'm guessing its really only detectable out on the highway at cruise. you would get better fuel mileage and probably run a little cooler.

[JeffBowlsby]

In the wild and crazy portion of my mis-spent youth I once tried the 1973 2 port TB vs the stock 1-port on my 74 2.0L 'performance upgrade'

The performance difference was awfully subtle. Maybe in a lab hooked up to wires and test equipment there is a difference but not the butt dyno. Underwhelmed if not unnoticeable.

[wonkipop]

In the wild and crazy portion of my mis-spent youth I once tried the 1973 2 port TB vs the stock 1-port on my 74 2.0L 'performance upgrade'

The performance difference was awfully subtle. Maybe in a lab hooked up to wires and test equipment there is a difference but not the butt dyno. Underwhelmed if not unnoticeable.

the old butt dyno would be fully trustworthy. (IMG:style_emoticons/default/biggrin.gif)

its easy enough to do on a L jet. i guess i should try some time. pull out the advance hose and plug the throttle body and see what happens. too lazy. car runs too nice.
might upset the apple cart. but i'm think i won't even notice the difference driving around town. not like there is any steady state cruising highways around here - even the freeways are clogged with stop and start traffic post covid. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/smile.gif)