Hi Everyone, This vacuum connection to the weber carburetors has been talked about 100 times, but I need to address it again.

CAR/Engine:
1) Porsche 914-4: 1975 1.8L big bore build, dual IDF 40 Carbs

2) I have Weber 40 IDF 19 's with no vacuum port

3) I have a Pertronix 1 SVDA Distributor, 12 VOLT with electronic points

4) I have two sets of intake manifolds
- One set has a port already drilled and plugged see photo
- The other set does not have a hole/port

5) Since my new Pertronix 1 SVDA Distributor, 12 VOLT has the combination of centrifugal and vacuum advance installed.

6) Can I just remove the plugs in the intake manifold and add the vacuum line with a "T" back to the distributor?

7) That's the way it is connected in my 1974 Porsche 914-4 2.0L car, except the car has dual weber 44 IDF's with a vacuum port on the bottom of the carb itself.

8) Please help, I'm in the middle of my build and coming close to installing the carbs, intake's, and distributor.

p.s.: I have two sets of intake manifolds, the holes that connect to the carbs are different on the two sets.

- 48mm for the short ones
- 40mm for the long ones

The 48mm ones were on the engine with the weber 40 IDF's
The 40mm ones were on a car with Weber 44 IDF's

The 48mm ones have the port driller and tapped.

Will it matter which one i use>? 40mm hole or 48mm hole?

Use the ones on the right as you won't want to install a long stud or bolt. I don't know why they ever manufactured those, maybe some one else knows.

For the port you will want to do exactly that drill one in the pic. Just one will do on #4 cylinder. Per John from ACN you will want a one way valve installed in line to keep the pressure consistent.

Click to view attachment

Look at my carb! no where to drill, i should be able to add the vacuum port to the intake on both sides, right?

You want the vacuum port for advance to be above the butterfly on the carb. That way it pulls vacuum as you open the throttle. Ports below the butterfly are for vacuum retard.

I guess i'm screwed. Can't really drill into the carbs!

Check out this thread and especially the last post: https://www.thesamba.com/vw/forum/viewtopic...e08bc9f7ed5c6dc

There is also some good info on this thread but it also goes on a confusing, and I think misleading tangent about ported vs. manifold vacuum, but there is some good info on drilling carps for ported vacuum that don't have the boss. http://www.914world.com/bbs2/index.php?showtopic=162620

Bottom line is that you can still do it.