Carburetted E9 - Vacuum lines - what is correct?

[Eivin Hansen]

I am strugling with the correct ignition timing, and I suspect the vacuum connections. I am running Pertronix Ignitior points replacement and have disconnected (and plugged) the retard port on the carb as per recomendations in posts here.
So after rebuilding my carbs i connected the vacuum lines as described in the original repair manual
http://e9-driven.com/…/Library/BMW-E…/pages/en/12110600.html and the car runs as shit when i set the ign. timing.
But then i find this description in another section of the same book (oficial BMW book) http://e9-driven.com/…/Library/BMW-E…/pages/en/13111000.html Whaaaat.. it is totaly opposite. I have tried this setup, and not much better, but i have not adjusted the ign. timing....

So what is correct? And recomended when using Pertronix ignitor?

As far as i know, the advance vacuum port on the distributor is the port pointing away from the distributor. sucking the distributor plate counter-clockwise. And advance port on the carb. is the one pointing 45 deg forward/right, where there is no vacuum when idling....Correct or...?

Another strange vacuum issue...the vacuum port on the carb facing to the driver side. (no 4 here: http://e9-driven.com/…/Library/BMW-E…/pages/en/13111000.html) is manifoil vacuum. and it is just fed directly into the air filter housing.... this is just like creating a massive vscuum leakage. Can anyone explain the rationale for this setup?

 

[HB Chris]

Manifold vacuum is retard, advance is above the throttle plate. If not using retard then it must be plugged at the manifold. When setting timing plug the advance line from the carb at the Dizzy.

 

[lloyd]

I am unable to view any images at present, but I would like to suggest you try posting photos of your setup. I would assume that you have a Euro spec model. Can you confirm that you have original Zenith carburetors, or is it possible you have replacement Webers? The porting is similar but not identical. You also have to bear in mind that different models, and in particular, models exported to North America would likely have additional porting than Euro spec models. For that reason, not all of the advice, to which you might be referring, would apply to your vehicle.

Regarding your last point and a massive vacuum leak, plug the line until you can find the source of the leak to seal it.
http://www.e9coupe.com/tech/zeniths/bmw1/bmw1.html
http://www.e9coupe.com/tech/zeniths/bmw2/bmw2.html
http://www.e9coupe.com/tech/zeniths/haynes/haynes.html

https://e9coupe.com/forum/threads/help-vacuum-connections.7015/

 

[Stevehose]

#4 should be a ported vacuum (same for the advance) so that when the throttle plates open it pulls in vapors. Should not leak at idle and won't create problems like an uncapped manifold vacuum source would. Cap any unused vacuum ports at the carb. Disconnect and cap the distributor advance vacuum when setting the timing. I eliminated the retard vacuum circuit as this was used for emission reduction at idle and will make you car run hotter. As for the pics, the correct manifold vacuum port(s) are located below the throttle plate (closer to the engine side) and the ported advance vacuum is located above the throttle plates (closer to air cleaner side).

 

[Eivin Hansen]

Sorry for the unclear description. Here are som more details.
The subject is a stock 1975/9 Euro (Sweden) 3.0CS with the original black tag Zenit/Inat 35/40 carburettors. These are rebuild just now.
The ignition is updated with new pluggs, cables, rotor, dirtributor cap, Pertronix Ignitor points and pertronix ignition coil. The vacuum advance mechanism is working and the same is the speed driven advance ( weights) inside the distributor.
But when setting the ignition as described in the book. (1700 rpm. plugged advance and 22 deg btdc. the shiny ball) the car runs very uneven.
So i am trying to eliminate any cause. Thus todays investigation is vacuum. where the original BMW workshop manual has two oposite descriptions (section 13.11.100 and 12.11.060
My throttle plate has 3 vacuum ports.
In this picture they are No1, No2, No4. No 3 is plugged from factory.

I beleive that i should be connecting No1 to the Advance port on the distributor. Correct?
I beleive that i should be connecting the No2 to the retard port on the distributor. Correct? (or is there no need for retard so i can cap the port No2?)
Port No 3 is not present on this model
Port 4 is combined between carburetters and then connected to the airfilter housing. Which is in acordance to the book. but why? it is manifoil vacuum. into airfilter? it wil create excess air into manifoil in the same way as a leakage.

The reason for the confusion is that i connected in accordance to this picture.

Which is part 12.11.060 (page 12-11.2) in the workshop manual.... Which is oposite the above picture, part 13.11.100 (page 13-11.8) in the shop manual.

 

[lloyd]

Stevehose observed that the manuals are not always the easiest to follow. The last time I was concerned with Zenith vacuum porting, Amundsen had not yet reached the Pole, so I have not much specific advice to offer at this time. As a short term measure, to get the engine running smoothly, a little trial and error may be your best bet, by experimenting with the two or three fittings you think are the source of your problems. Consider taking up golf and collecting a handful of wooden golf tees and systematically plugging any vacuum hose suspected of leaking vacuum or piping vacuum to any equipment that leaks, e.g., the air filter housing vacuum fitting mentioned. HBChris described “ported” vacuum sourced from above the throttle plates, which of course, supplies vacuum with the throttle open. There may be a port that supply’s interim vacuum, when the throttle is just opening, but I cannot recall that this exists on your carburetors. The only other porting would be manifold vacuum.

While vacuum can be essential to decent engine operation (mostly part throttle), you mentioned your carburetors were recently rebuilt. How did the engine run prior to the carburetor rebuilds? (While it is presumed that the carburetors were properly rebuilt, a thin gasket placed upside down or maybe even intended for a different model carburetor, can alter vacuum porting. Float settings can also affect carburetor function, despite vacuum routing.) The vacuum advance attached to your distributor is important for proper engine operation. Have you checked the vacuum advance mechanism for proper function? Is it possible that vacuum pot is not holding vacuum? Have you tried running the engine with the vacuum advance disconnected?

I suspect, our friend, DeQuincey, has posts and a video on this subject.

 

[Stevehose]

Lloyd, ported vacuum supplies vacuum when the throttle is open, manifold vacuum provides it when throttle is closed. Elvin, you'll have to visualy inspect the ports to see which are manifold vs ported based on their position relative to the throttle plate. For ported vacuum you may be able to see a tiny hole on the other side of the take-off pipe in the throat of the carb. Or use a vacuum gauge as Lloyd illustrates, manifold vacuum will show a reading when at idle, ported will show no reading. Opposite when the throttle is opened a little.

 

[lloyd]

Lloyd, ported vacuum supplies vacuum when the throttle is open, manifold vacuum provides it when throttle is closed.

You are obviously correct. Prior post corrected.

Maybe time to switch to decaf or fire the cat as a secretary.