manifold vacuum

[btl069]

would anyone know if the small vacuum tube found on a dual port intake manifold be enough for the automatic's control valve?

picture below with arrow pointing to the small tube I'm talking about.

thanks

[Eddie]

From what I can tell in your pic, yes. That is where the larger vaccum line is hooked on mine. It runs from there to the control valve.

[btl069]

Hi Eddie,
are you still using the original single port intake manifold with the larger vacuum tube?

Just to be clear, was your answer a "yes" that smaller tube would be enough to work with the control valve?

I obviously need to use an inline adaptor between the the control valve & the manifold if using the smaller tube is sufficient.

I'm just worried that switching to a dual port intake manifold with the much smaller vacuum tube might cause problems later on.

thanks

[Eddie]

I may have misunderstood what you asked. I have a small hose that comes from the control valve [I guess] that hooks to the vaccum on the carb. There is another larger hose that hooks to the vaccum on the dual port manifold right under the carb. I have another vaccum port on the intake manifold between the carb and head but it is plugged off. Hope this makes sense.

[Eddie]

Sorry, I did not say but I am running a dual port. With the small vaccum hooked wrong on the carb, it will shift with a jerk. The big line goes to the manifold.

[Bookwus]

Hiya btl,

The small nipple intake manifold will NOT work with the AS control valve.  You will need the large nipple.  Finding a dual port manifold center piece with the appropriate port/nipple might take a little bit of looking.  But such manifolds should be found at a large online VW boneyard like Way Out.  Or you could do a little metal work on a regular dual port manifold.  There is even a third option..........in 1971 VW installed a brake booster unit in the Type 2.  It required a vacuum assist and uses the same manifold (albeit a different VW parts number) as a dual port AutoStick.  Matter of fact, that's what I'm running in my car right now.

[btl069]

Hi Mike,
aside from the physical difference in size between the larger control valve tube and the smaller intake manifold tube, why wouldn't it work? Not enough vacuum due to the smaller tube?

thanks
dennis

[Bookwus]

Hiya btl,

Exactly the case!

The smaller port will act as a restrictor.  And do understand that the vacuum drawn from the manifold port not only travels to the control valve, but from that point moves along to the clutch servo which activates the clutch.  And...........  the same vacuum also "charges" the vacuum can found under the left rear fender.  Restricting the vacuum flow in any way (that's why it's always a good idea to check your vacuum hoses) will compromise the entire system.

[btl069]

thanks for the help guys.

not the answer I'd like to hear as that means I have to disassemble the bits to have the manifold modified. but, if it has to be done to have it working properly, then so be it. fortunately my engine is still out of the car. It's still a lot better than finding out later when the engine is installed.

thanks again gentlemen.

dennis