Had the car in for a post PI today and tech noted that the "vacuum advance" on distributor was not connected when the (previously bad) charcoal canister was removed. He teed into another vacuum line and connected the vacuum port. He noted that this will increase RPM's but will also help with acceleration.

I did notice a slight increase in acceleration but more so, the car is now idling at 1,600 RPM when warm. Seems excessive. Plus, I think that I noticed that the exhaust no longer "pops" when decelerating (which was kinda cool...yet slightly obnoxious).

Thoughts? Thanks for educating this Newbie...

the vacuum line from dist. goes into the throttle body.
on its own and not into anything else.
but i have a 74 1.8. maybe its different.

I don't think a 75 had advance, at least not the 2.0, 1.8 could be different. If it does it definitely doesn't go to a t. Port just above the butterfly on the tb is the only appropriate place. That port is gone post 73 on 2.0s. is it the original distributor?

Oh, and your high idle is due to your advance being "advanced" at idle I suspect. Set up correctly it will only advance at partial throttle.

You should not be idling at 1600 RPM.
If what the tech did actually corrected a problem he only fixed part of it.
There are several variations to the hose routing and I usually have to search the diagrams until I find one that has all the equipment the car I am working has.
Examples: Does it have EGR? Does it have Air Injection? Does it have the charcoal canister in the engine compartment or in the frunk? A You need to verify the equipment your 1.8 has and then make sure the vacuum lines are routed correctly. Then check and adjust your timing and idle speed.

Good Luck
Jim

Thanks Jim. The car had a charcoal canister that had been taken off because it was deteriorating. The tech did something with those lines after deciding to not reinstall the canister.

I'm taking it back tomorrow to be checked out and probably reverse what he did. I don't know enough about this car yet to do the work myself. I appreciate your feedback!

hopefully he capped the lines to the can as you would expect a tech to do.
---and did not re-route them into anything else.

i think i have read something about one vacuum line from the distributor in some cars (later 1.8 L jet) which is not meant to be hooked up, it just is there but goes nowhere.

some 74 1.8s definitely have the green line from the distributor (at the base of the dist) hooked up to one side of the throttle body and the upper line from the distributor hooked up the other side of the throttle body.


some diagrams are here with some discussion about charcoal cannister plumbing.
http://www.914world.com/bbs2/index.php?showtopic=347951

i will see if i can dig up the discussion i thought i read about the unconnected vacuum line. i don't think that was about 2.0 D Jet cars, fairly sure it was something about some 1.8 L jet. but emorygt350 is talking about the same thing in post above - it could be 2L cars that have the hose that goes nowhere out of the dist.

Given it is a 75 1.8 L jet it definitely has the can in the engine bay and directly beside the battery.

correction mate.

i lie about the distributor vacuum advance on later 1.8s.

i went to mr. bowlsby's website for you.
he has some vacuum line routing diagrams for the cars there.
v. useful resource.

https://bowlsby.net/914/Classic/TechNotebook.htm

only the 74 1.8s have both lines to the distributor directly.
(though there is a variation on that with an open line from distributor that is shown in this diagram. i have the one where both run to the TB. complicated isn't it?).
pretty sure this is the early one with open line, that is close to what i have and was talking about. at some point in 74 they run both lines to the TB.
Click to view attachment

this is the later one, noted from about mid 74 on.
but i think accurately it is the 75 model year with EGR.
the vacuum line is hooked up to a T.
(learn something every day - the cars constantly changed! - emissions regs?).
this is joined to the later type of ex. gas recirc valve.
your tech does know what he is doing if he hooked up to that T.
and that explains why your exhause is not burbling anymore.
they pop a bit without the decal valve and probably egr valve hooked up.

Click to view attachment

the high idle is due to something else.
as per suggestions above.
your tech should be able to sort it out.

---

if you do put the can back on there is debate about the can plumbing.
some here have the view that the can is plumbed according to the diagrams on mr. b's website. others, like me, think the plumbing to the can changes when it goes into the engine bay. the explanation to me is simple. cans in the front trunk were plumbed up porches way as per 911s to 1974. cans in the engine bay were plumbed up VWs way which was always different to porsche. the discussion around that is in the link to the thread in my post above. its a bit academic. but i am sure the can works better if its plumbed to work the VW way.

The key here (as others have said) is where the distributor vacuum lines plug into the throttle body. Vacuum advance (that comes off the front cone side of the canister, should plug into port vacuum that is just ABOVE the butterfly. Vacuum retard from the back (flat side) of the canister should go to manifold vacuum on the throttle body BELOW the butterfly.

As has already been described, port vacuum comes on as the throttle begins to open to kick in advance for faster acceleration, but should not affect idle speed. The retard helps SLOW idle speed. I've also read that some MY 2.0L cars didn't have the vacuum retard connected but I believe all had advance connected. My 73 2.0L had both sides hooked up and I have them both working on my carbed engine now. The retard really helps with a low, smooth idle and the advance makes for crisp acceleration. It sounds to me that the tech has your advance connected to the wrong port. I also agree with the comment that once you have the vacuum lines hooked up correctly, you'll need to readjust the timing (with the advance and retard hoses disconnected and vacuum ports plugged. Then reconnect the hoses and adjust the idle speed.

Exactly. When I reverse my retard and advance hoses my idle jumps to 1500-1600. Ask me how I know....

Many post 73 models just left the advance unattached apparently (smog?) but kept the retard. On a 74/75 I was just looking at the actual port on the TB was cut off and filled. Now 1.8s are different, but if you have both advance and retard I would (as the diagram shows) be very careful about which port your two lines go into. You could have this fixed in two seconds if this is in fact the issue.

Many thanks, gentlemen! I will get it sorted out tomorrow and report back. I really appreciate your assistance.

Wanted to report back that my TB only has ONE port. All proper connections have now been made, car idles properly and that the extra connection off the distributor (shown in diagrams going to the 2nd TB port) has just been left open. I may eventually stick a 3" hose on it and let it "twist in the wind" as others have noted was the factory setup.

To repeat - my '75 1.8 engine has only the SINGLE PORT on the Throttle Body as dr914@autoatlanta.com stated was the case.

Thanks again for everyone's assistance!

Awesome. Very understandable that a Mechanic would assume it was an advance.

nice work mate.


my car / jan build 74 1.8 / is two ports. orig tb, not a replacement.
diagrams floating around need some more work to get accurate?

I don't really know what 'late 74' means but I think the diagrams posted above show the two variants pretty well. Lord knows which you end up with but if you have the ports on the tb it does show you what to do with them.

Although, looking closer, it is interesting that the retard switches ports. That doesn't make sense.

yes, something not quite right with diagrams.
unless ports exchanged sides on which was an advance and which was a retard port on the two different throttle bodies? i have never seen a single port throttle body - don't know.

here is a post i found - dave darling/shop talk forum/20 years ago.

my 74 set up agrees with second diagram showing 75 cars except there is no EGR valve.
so plumbing hook ups with ts to TB lines and CV line not there.

Since it seems to be working that port couldn't be advance, since it would get no vacuum at idle. I would still double check for 'science'. If you get a chance, pull the hose at idle and see if it has vacuum, if so it is the retard port. Someone with two ports and a functioning engine should try the same. Egr makes sense attached to the advance circuit since you only want gasses coming in at partial throttle cruising.

@emerygt350 ....that 74 hose diagram above is wrong.

attached is another i found.
this agrees with my jan 74.
advance and retard lines correctly hooked to throttle body for advance and retard ports on throttle body. vac lines agree with 75 diagram (except no EGR yet).



Click to view attachment


the diagram is marked up with amendments to charcoal can plumbing with Xs and revised line layout by @Starbear . he has an original 74 1.8, same as me,
the diagram and discussion on charcoal can are in thread link below.

some of the diagrams floating around have errors in them as a result of assumptions relating to earlier cars and possibly owner alterations/mods?

http://www.914world.com/bbs2/index.php?showtopic=347951

That makes way more sense. Good.

i found this.
got curious about advance hooked up and retard left open on some L jets.
i shouldn't as sometimes its better not to think about EPA bone tipped spears and flint axes and just be dumbo.
i annotated it for translation.

Click to view attachment


since i'm locked down in the worlds most locked down city its giving me too much time to think and not enough time to

if i understand the diagram right whats going on is if you snap the throttle shut on a 1.8 L jet with two vacuum lines from the distributor type of set up then the engine suction alone on the retard line is going to pull the retard back further than the at rest position at idle (it goes past where the springs would reach equilibrium). then as the vacuum weakens (revs come down) the springs take over again and advance the timing back up to idle position. the normal vacuum advance is completely closed by the snapped shut throttle. (an emissions thing on deacceleration if you close the throttle completely?)

this seems to correspond with how my car behaves particularly during the time the car is cold and warming up. if i give it a bit of a squirt before i drop the clutch, often just when i am moving it out to the door of the garage and close the throttle sharply it almost dies and then comes back up to idle. maybe they unhooked that vacuum line at some point in the production run to "cure" this behaviour so it just retarded down to idle setting where the springs equalise and no lower?

or conversely they never had to do this before the end of 1973 but had to introduce it at the start of 1974 to meet the emissions regs. when do they kick in? calendar year?

It's in idea. I suspect the springs are primarily there to center the advance arm, although overshoot is possible I suspect even idle engine vacuum probably pegs the retard (on the bench it doesn't take much to peg it). The decel valve also works with that rev down stuff.

My car does undershoot idle by a couple hundred rpm and then rise again but I don't mind since I find a hung idle to be super annoying. Not sure why. I would rather go low and come up then hang high and slowly come down. You could probably see that overshoot on a timing light.