Tired of vacuuming

 Good evening all,

Been sorting a few niggles on my mk1.

Its a 1983 Gti tin top, 1.8 dx engine. Engine wise completely standard.

I have noticed the idle is a bit high, so was looking through the vacuum lines etc. and started to look up a vacuum line diagram from the web.

The issue is that mine seems to be different to all others I can find.

My dizzy only has one nipple on, and the line that runs off it goes to the back of the throttle body underneath the idle screw.

The small plastic part that everyone seems to have two vacuum lines running off (one to the dizzy to a second nipple on the dizzy and one to the MFA) on my car only has one line attached which goes to the MFA with the other blanked off - with what looks like a proper blanking part.

Can anyone shed some light on what is going on, the outlet below idle control valve to which the dizzy is currently connected appears to have no vacuum, so I'm assuming I have no vacuum advance on the distributor?

Anyway, pics below to try and explain by jibbering and what I dont have.

That should be to the up shift light on your dash IIRC.
If you don't have a upshift light in your cluster then you don't need it.


Or it is the on/off for your charcoal canister.

Briano1234 said

That should be to the up shift light on your dash IIRC.
If you don't have a upshift light in your cluster then you don't need it.


Or it is the on/off for your charcoal canister.

Thanks Briano, I've seen that diagram you posted too.

Again it shows a vacuum line both too, and from, the dizzy.

How come I only have the one to the back of the throttle body? And am I missing advance because of this?

Well with the various owners of cars, you never know what the POS (Previous Owners Servicability) did.
I know who things should be… Not how they are currently.

That Vacuum switch was only on Manual Transmissions after 1981 over here.  IIRC the 82 Rabbits had it as a great example on how to increase your Mileage by telling your when to shift.  In 81 I think I knew by then on how I wanted my cars to shift, and besides at 55mpg on my diesel did I care about 1-2mpg difference.  

I guess my question is, should I return my setup to standard?

There must be a reason vacuum advance on the dizzy is required, does it not change the ignition timing or something?

My car does seem a little flat power wise.

I think they used the Dual port diz as a feed through to keep the Heater control units operational.  But to me if you had the dual port and leaky Heater servos, then rough engine running would occur.  Which is why I think they changed over to single port advance before the advent and better use of a Hall Sender operation which didn't get effected too much by loose vacuum hoses.

What you have described is stock set up.
How do you know you have no vacuum at the throttle take off?

When I converted my Vac Res from Balls on the hood (Egg Crate) over to Large canister Check Valves, Upon Rapid Acceleration (Stomp on the Gas, or Downshift and Stomp the Gas) I noticed a severe drop in the Vacuum to my heater box from full front to defrost momentarily.

So while you have a decrease in Vacuum from the rapid intake of air (Overwhelming the Vacuum over the venturi in your Carb or Throttlebody) it will resume when the engine then achieves its new Stomp designed RPM and the Air flow that has increased is now constant but at a higher level.  

Knowing what your Vacuum is at idle, then Stomp it you would see that it ebbs, then resumes (ebb as in gets momentary goes Positive in stead of Negative).

I always could tell a Vacuum leak with my ears in the old days and I had good Hearing after having to be seated under the noise of listening to Radios, and Turbine engines above me for a few years, my hearing has decreased where I now use other ways to find a vacuum leak.  

They are: Fluttering servos for my heater box on my dubs, or the Vacuum pump on my Diesel dub failing.

If there is a vacuum leak I usually have a engine that can stumble or act different.

Spraying WD-40, or Carb Cleaner on my vacuum hoses causes a increase of RPM (usually on my hose connections.

Smoke Testing it.

I have a good track record of Seat Of the Pants diagnosing these things.  I used to have a Toyota, and when the RPM acted a tad off, or the engine wold sound lumpy, I took out my Pair of Diagonal cutters, and trimmed the ends of all my Vacuum tubes and that usually corrected the errant behaviors.

With Prior Knowledge of Lucas Electrical systems, and then transitioning to Bosch's Version, I have learned that
If Lucas was the Lord of Darkness, then Bosch was his Prince, and the quality of your grounds on Electrical systems is imperative to proper running of all things

My attempt at humor hope it helps you, and clarifies my take on things.  

paceman said

What you have described is stock set up.
How do you know you have no vacuum at the throttle take off?

Thanks Paceman.

So stock that they only have one vacuum connection, that's interesting.

I know because I can pull the hose off and theres no vacuum and idle doesn't change.. Is that weird?

If I pull the mfa line or blanking plug off the plastic manifold think I can hear the vacuum and idle drops.

Connect the dizzy to the plastic manifold and it goes through the roof.

You will have much less vacuum at idle when using the port on the throttle (this is ported vacuum), the other vac take off (that goes to the MFA) is manifold vacuum, this is higher at idle. You can go down a real wormhole reading about manifold vs ported vacuum…. Don't ask!
The best way to check for advance is with a timing light. Ignition timing should be set with vac disconnected for the dizzy, then with it connected you should get some slight advance.
Do you have a std cam in it?

paceman said

You will have much less vacuum at idle when using the port on the throttle (this is ported vacuum), the other vac take off (that goes to the MFA) is manifold vacuum, this is higher at idle. You can go down a real wormhole reading about manifold vs ported vacuum…. Don't ask!
The best way to check for advance is with a timing light. Ignition timing should be set with vac disconnected for the dizzy, then with it connected you should get some slight advance.
Do you have a std cam in it?

That makes sense! Thanks for your knowledge….I feel like I'm learning.

Yes standard cam as far as I'm aware. I was literally looking for a timing light yesterday as that's next on my to do list. I know all the mechanical timing is bang on as I did the belt recently.