I know this subject has been beaten to death and there is a ton of information on the internet, I have done my home work, but I have a simple question. I realize the typical culprit of high idle is vacuum leak or timing. All vacuum leaks have been chased down, valves are adjusted, all usual parts have been replaced and car is tuned. Here is the question.

I removed the vacuum lines (2 each.) from the distributer and set the timing at 26 BTDC at 3000-3500 RPM (full advance) as per the manual. Idle air crew is tightened all the way in (CW). Car idles well at 800-900 RPM, revs well and sounds good. When I reconnect the vacuum line to the distributer diaphragm (what I would call the front side, furthest from the distributer), the distributer advances and idle raises to 1200 RPM. This line has pretty good suction and runs to the intake plenum. It seems like something is wrong inside the distributer, week springs on advance plate etc. but I'm not real familiar with these fuel injection distributers.

Currently, the line is plugged and disconnected from the distributer. The car runs and drives fine and idles well hot or cold. At cold start (Arizona cold 40-50 F) it idles high as it should then settles down as it warms up. However, I don't like to operate vehicle's "rigged" like this. I want the line hooked up and operate normal.

Thanks in advance for any insight,

Mark O.

Sounds like you have the retard and advanced mixed up. Try switching ports.

Sorry, just reread that. Sounds like you have hooked the advance to the plenum. That needs to be on ported vacuum from the throttle body. That should only have vacuum when you crack the throttle. What year is it? Some years don't have advance and retard.

Probably useless for me to chime in since I'm only familiar with 2.0 Djet, but I would think the idle should be higher than normal after timing it until you hook up the retard line. It also shouldn't matter that the TB idle adjustment screw is closed all the way when timing it since you're opening the throttle plate when revving to ~3200kRPM.
I would expect you to maybe have to crack the idle adjustment screw just a bit to keep the idle from being too low when it's all set correctly.

Do you have the vacuum lines to the distributor routed correctly? Also check the diaphram itself. You should be able to pull slight vacuum on the distributor with a vacuum pump with the distributor cap off and see that it's working.

First off, you need to remove and clean and regrease the advance plates in the distributor. that 40 year old grease is more like glue now and you will never get a consistent advance response.

Secondly...the system (1.7 Djet) does not really need vacuum advance.
But, if you insist, as stated above...you have the hose connected in the wrong place.

I personally had this motor...I unplugged and capped all the vacuum lines related to distributor advance and retard.
I cleaned the advance plates and applied new grease. ($0.05 cost)
Ran like a top, idle is manageable very easily with the idle adjustment screw.
Retard snaps right back, as designed.

http://www.914world.com/bbs2/index.php?sho...c=70988&hl=


Rich

What he said. Cleaning and regressing the distributor is an easy job that makes you feel good (and should be done).

Or you could just spring for a 123 dizzy and say goodbye to all this nonsense.

not sure why you guys are so down on vac advance?

i can only speak for L jet but i'm pretty sure it works the same on D jet.
and it was a pretty common device for just about all VW engines through the 60s and 70s, even the carb ones we had down here. it helped to smooth out the throttle response up at cruise speeds and meant the engine ran slightly cooler at cruise. it also delivers fuel economy gains at steady state cruise because it will advance the timing way out and does so quite safely. the minute you open the throttle a bit it comes straight off.
and when you close the throttle it come straight off instantly.

vac retard, thats another matter and was pretty unique to USA engines.
the old double vac can distributor.
the retard is there for emissions. at idle for most of the cars.
though the later 914s for california from about 74 on and rest of USA from 75 have retard only. the advance vac can is not even hooked up. which means those engines are retarded at steady cruise as well. for emissions!!!!!
its not so good. causes the engine to run hotter. to lower NOX at idle and at cruise.
rest of the time it is not actually on.

so an advance vac hook up is generally a positive thing.
if the distributor is still in good working order to go with it.
hooking up the vac advance correctly in this case would be good for fuel economy at cruise and slightly cooler running at cruise as a bonus.
not sure on how 1.7 D jets hook up but i agree with OP in his desire to hook up vac advance if that is what he is trying to do.

all i can offer is that on the L jets the advance vac hose connected to the front side of can (the bigger section of can furthest from distributor body) is hooked up to the throttle body port above the throttle plate. ie before it gets to throttle plate and plenum.
has no effect on advance until throttle is open and there is partial engine vacuum.
ie steady state cruise generally. the retard is hooked up the smaller side of can and connects to the throttle body after the throttle plate. that means it always works every time there is engine vacuum. ie at idle with the throttle closed. thats when it retards the engine, makes it run hotter, produce less NOX and would be utterly hopeless at taking off from the lights. except soon as you open throttle vacuum drops and it snaps straight off and off you go. it also operates at cruise but the nett effect is vac advance - vac retard = actual vac advance. the advance side is much stronger than the retard side.

not down on vac advance, but as I said...its not needed.

But..

the root cause here is two things.
Dirty advance plates.
Hose hooked up to the wrong source location for the advance diaphragm on the distributor, thus adding too much vacuum.

i think you are right.
the centrifigal mechanism may not be operating at optimum anyway.
and if the vac stuff is sticking it can't be good.
i was qualifying it by saying if the distributor was in good order.
which by now in 2023 is a tall order.

i don't know anything much about D jet at all.
its even more primitive than my dinosaur.
but very interesting because of that.
the little old distributor is pretty important to both of them functioning well half a century later.

go read the link I posted above.
Also, Ray Mital may have posted an even better thread with pictures to show how its done.

they are pretty simple to take apart and clean.

rich

Thanks for all the quick replies. As I was writing this original post, I wondered if the two lines could be backwards as the hose to the plenum has much more vacuum at idle. I purchased the car this way. Probably why the idle screw is all the way in as previous owner or tech was trying to get the idle down. Ill try swapping the lines when I get back in town and report back. Thanks again.

Don't swap. Neither should be going to the plenum. Send us a picture of the engine bay. We can verify the hoses. What year?

yeah. strictly speaking that would be correct with the factory set ups i know of.
but having said that, its quite possible to run the vac retard side of can to the plenum after the throttle body and throttle plate. its going to have the same effect. and i do believe i have seen some 1.8s lashed up that way for whatever reason.
the advance side of can should definitely not be hooked up to the plenum. that would make absolutely no sense with the way the VW system is meant to operate.

i had a look at @JeffBowlsby 's site where he has an early (70-71) 1.7 hose diagram.

https://bowlsby.net/914/Classic/zTN_FI_Hose....7L_1970-71.jpg

in principle it seems to be the same as the later L jets like mine.

retard side of can is going to a port on throttle body which is on plenum side of throttle plate.
advance side of can is going to a port on throttle body which is on air intake side of throttle plate.

that would make a lot of sense to me.
classic VW strategy on the vac advance.
and looks like even then there was a kind of emission thing going on with the retard vac can? it would be the only vac operation on the distributor at idle.

heres the hoses in the factory manual.

i ain't seeing nothing there that differs much from L jets with the distributor vac hoses.
and it corresponds to standard vac hook ups.

looks like they changed the throttle body along the way and fiddled with where the two ports were on the throttle body.

definitely no vac hose from distributor into plenum. both go to t/b.
its a matter of getting the correct hose on the correct port on the t/b.

Click to view attachment

Click to view attachment


and as @r_towle notes. making sure the whole mechanism slides easily down there in distributor. lube and clean etc. sometimes of course the diaphragms can be cooked inside the vac can by this time of life.

Plenum and just under the plates are different. You want the weakest vacuum possible on the retard at throttle open. The advance side is set to overpower the retard side. Others have described the interesting design in detail elsewhere.

Still hoping to hear what year.

a thought.
don't know which 1.7 this is. not stated by OP.
but there was a special one for california in 73 - the most pissweak of all.
which i know nothing about. but someone will.
but i'd be prepared to guess it could possibly not have had advance hooked up.
certainly 74 cal 1.8s did not have advance hooked up. it was a dumb as just plugging the port on the throttle body and leaving the vac advance side of can open to the atmosphere, by tucking the bit of hose under the plenum.
and all the 75 1.8s USA wide did not have advance hooked up.

emissions.

sh#t of a system if you ask me.
the cars lucky enough to have advance and retard hooked up were a nicer compromise.

yeah, that was us discussing the dizzy design in the L jet thread a few years back.
going through Van's relentless purge of decaying L jet components.
a lot of folks have a simplified view of the vac can. as if its only got one membrane.
not so. its way more elegant and complex than that.

i'd agree with you about just near the plate.
thats where the factory put them.
but i have seen 1.8 lash ups.
probably because they sourced throttle bodies from elsewhere off other cars and had no retard port on throttle body. not sure why. but there were lashups floating around on BAT ads and other for sale documentation. that retard port on the t/b is pure american market.
along with the double can distributor!

@emerygt350 - reading @Aeromek 's first post again its actually pretty obvious its all mixed up.

i imagine its very much like an L jet now that i have looked at the hose diagrams.

you tune the L jet with the vac hose off the retard at the distributor and with hose plugged. you set the timing and get the idle steady at about 900 rpm.
then you plug the hose back on and the retard kicks in. usually the idle should go down and become a little less steady. so you give the idle screw a bit of turn and adjustment and get her steady again around 850 - 900.

aeromak's idle went up when he put the hose on. pretty obvious it instantly advanced the timing a bit. if he had it right it should have gone down and he would have needed to bring it back up. thats if its anything like an L jet. and i don't see why it would be different.

nothing should have happened at idle when reconnecting the advance hose if it had been off for setting timing.

Thanks again for the added info. above. All great info. and all makes sense. Haven't had time to clean and lube the distributer yet, But I did swap the hoses. Didn't help much as both have a significant amount of vacuum. In doing so, I found an open port on the throttle body. I see the reply above with a diagram that shows both hoses going to the throttle body (not the plenum). The diagram isn't very clear which port goes to retard and which goes to advance. I realize the lesser vacuum should go to retard, but thought someone might know which port go's where. One port is vertical (points up) one is horizontal (point out the side). So question is - Horizontal port to advance or retard ? Vertical port to advance or retard ?

Again, I bought the car this way, so just trying to figure it out. Still idles and runs fine with advance line disconnected and plugged. Car is a 1972.

OFF SUBJECT, is there a way to set my notifications in this forum so I receive an email if someone replies to this thread ?

thanks again

Think about it. The throttle has a throttle plate. When closed, there are two ports. The port behind the plate has the highest vaccum AT IDLE when closed. The port in ADVANCE of the plate has the least if any. Imagine the plate in slow motion opening and what happens. So the port behind the plate is the retard port and the port towards atmopshere WHEN closed is advance. When partly opened the retard port starts to drop in HG and the advance starts to increases in HG. With the throttle plate fully open....both drop to zero.

Disagree with what Rich says....it is not worthless for a D-jet engine...in fact on part load when the engine throttle plate is only slightly open, the timing won't respond as quickly and for d-jet slighly lean....ping. Not good.

Check the vaccum ports on the dizzy vaccum can..both of them for holding vaccum like the MPS. If it won't hold vaccum it's junk and get a 123 distributor.

There is a drawging around here somewhere that shows this...from the factory manual.

@Aeromek

yeah, just put a finger on the ports while the engine is idling. If it has vacuum at idle, it is the retard port. If it doesn't it is the advance. I would get everything hooked up as it is meant to be and go from there. If both have vacuum check to see if your throttle is closed all the way and then look for other ports on the TB that might be heading off somewhere else. looking at that diagram for the 1971 1.7 makes my head explode. we need a 1.7 junky to chime in. What the hell is 12 on that thing? Why is the ported vacuum heading to that 12 thing before the distributor?

If the PO screwed this up, I would be super suspect about the rest. Make certain your decel valve and mps are all hooked up correctly as well.

Hopefully those diagrams wonkipop posted are accurate. The 2.0 diagrams out there are often not accurate.

I believe there is a setting that tells you when people reply, but it doesn't seem to work for me.

look at listed parts down bottom of diagram @emerygt350
#12 not on 914. don't trouble yourself.

these diagrams were often universal diagrams for anything VW with a D jet.
my guess is #12 probably has something to do with auto 411/412 cars.
but its only a guess.
eg. the L jets when fitted to some 412s are completely set up different to L jet 914s.
pretty sure don't have retard can in distributor, have strange spring loaded vacuum operated throttle stop gadget and have EGR coupled to run at idle.
all in the interests of the engine holding idle against torque converter when stopped at the lights ------->while keeping the EPA zealots happy.

hose diagrams are from the factory workshop manual.
but of course thats no guarantee of unclouded accuracy or not causing confusion.

correct ---> but only half the story.
the spring in the vac mechanism snaps off the retard as soon as you open the throttle from idle.
the retard at idle is there for emissions. at least in the L jet and i suspect the same for earlier D jet.
but you would never take off from the lights with the engine retarded as it is due to vac can. so.....its designed to immediately snap off. the minute you open the throttle to go.
the vacuum in the engine drops but its really the spring that snaps off the retard and snaps it off fast without the vac present, in either of the throttle ports.

generally the advance does not come into play until you are steady state cruising with the throttle only partly cracked open. then the vac builds in both ports as you suggest.
since advance can is bigger than retard can its designed to give you the kind of advance you would have gotten in much earlier VWs with single advance vac cans.
ie advance can - retard can = actual real advance --- which is added to where mechanical advance has the timing.
this vac advance can go way out there without danger of detonation etc since as soon as you gas for power to accelerate or deal with a load (say up hill) it again snaps straight off due to the spring, because opening the throttle drops the vac up around the ports.

that super advance the vac can delivers results in fuel economy enhancement at cruise.
and......cooler running.

the EPA tests/regs in the very early 70s were strictly concerned with diminishing emissions at idle. ie urban situations, stopped at lights, in traffic at standstill etc.

its in 74 in california and 75 states wide that the EPA went after cruise emissions as well.
ie freeway/interstate driving. hence the vac line from advance can was pulled out of t/bs and tucked under plenums harmlessly and the advance vac port on T/B was plugged or deleted. now you had a situation where the timing was only ever retarded slightly at idle or cruise. bad for fuel economy. engine ran at higher temps around exhaust valve and upper exhaust outlet pipe. but emissions lowered.

only you guys in the states got these double vac cans.

our VWs down here in aus had the simple vac advance cans only from the about mid 60s until the end of the air-cooleds in 76. absolutely no vac retard function in them.

The well lubricated weighted advance plate are what make it run properly.
Look at what the mechanical arm from the vacuum advance canister is attached to….the advance plates.

Clean, relube.

Unplug both lines
With thorough testing by plugging in one at a time, determine which vacuum controlled module is defective.

Distributor, decel valve, AAR, etc.
Many times you will find more than one component has failed or is leaking after 40 years

Vacuum advance is specifically designed for part throttle situations where you need more advance to ignite the A/F mixture at partial load…like cruising on the highway at a fixed speed, throttle just partially open.

Vacuum advance has nothing to add to idle when the throttle is closed.

Adding unmeasured or unaccounted for air into the intake system will change the idle speed and make the engine run fast and potentially too lean, so you need to find the air leaks.

Djet is kind of cool because it measures manifold air pressure to determine how much fuel is required.
It’s also not super accurate…version 1.0 of EFI really.

Exactly, but he needs to make sure everything else is hooked up right and then disconnect from there. I would make absolutely sure everything is perfect, then go ahead pull the retard. And the advance if that floats your boat. I wouldn't personally. I did find on my 2.0 the retard was not a problem at all after everything was working perfectly. Gave me a very nice idle.

Until I I got sick of trigger points and points and bought a 123 from tangerine.

Lots of advancements in tech but troubleshooting still just takes time and walking through each step.

Idle won’t fluctuate based upon the advance and retard hoses being removed from the equation, and plugged (for the test phase)

Then he can focus on finding the leak.

But….(broken record)
Clean the advance plates so they work perfectly, then ignore them for the test….

Good luck OP, it just takes time and patience to find vacuum leaks in old cars with 20 vacuum lines

Idle should increase as he removes vacuum from the retard.

I wouldn't even worry about leaks till you know everything is going where it needs to be going. At that point some carb cleaner can help you find leaks if needed.

From experience:

I chased a fluctuating idle and high idle for a month before I tested the advance/retard vaccum canister on a stock D-jet dizzy.

Check it for leaks first..otherwise the rest doesn't matter. Same goes for the MPS.

After that...I found a couldn't find a stock replacement for the vaccum canister...so I pitched the dizzy.

Sorry about that. I got one or two things backwards on early iterations of the diagram, and some copies of those are still out there.

--DD