Vacuum Hose Lines from Distributor to Throttle Body

[wrxnofx]

My '77 FI has a vacuum line that goes from the distributor vacuum advance to the throttle body:

However, in looking at the Type IV sticky, there is supposed to be a T that has an additional line going to the air cleaner:

Is that what this empty nipple is for on my air cleaner cover?

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1977 VW Type 2 Bay Window Westy FI

[SGKent]

yes but you need to suck on or apply a vacuum to both the distributor and canister purge lines to be sure neither diaphragm is perforated. The idea is that the ported vacuum (meaning it only exists when the throttle is open) doesn't bleed off because one of those diaphragms is bad. Both should hold a vacuum. Suck on the hose, put your tongue on the hose and see it if holds the vacuum, or use a mighty vac tool etc..
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[busdaddy]

And if the one on the aircleaner doesn't hold a vacuum (which is common and likely why it's bypassed) read this: https://www.thesamba.com/vw/forum/viewtopic.php?t=476758&highlight=eec+valve
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[wrxnofx]

Okay, I tested the vacuum on both the distributor and on the air box. The distributor retains the vacuum but the air box does not. I can hear the diaphragm clunk but it doesn't create/hold a vacuum.

Looks like I'm repairing that diaphragm. Thanks for the link, busdaddy!
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1977 VW Type 2 Bay Window Westy FI

[Slip356]

78 stock Westy with FI. Had the same problem which means you have no vacuum advance. I just removed the T in the hose, taped up the nipple on the air box and went direct to the dizzy. Really woke up the motor. Bentley has a neat chart that shows the correct full advance, vacuum & centrifugal for different dizzies.
Some say you’ll get a fuel smell on engine shut down. It’s been a couple years, no smell.
Try it you’ll like it!
Slip

[SGKent]

Colin used some red RTV to fix the air box diaphragm. 914 Rubber used to make them but I haven't seen them on their site anymore. There are two sizes of that diaphragm. It would not be hard to make a mold from one and pour a silicone diaphragm. They aren't that sophisticated.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin