L Jet vacuum leak pursuit '74 1.8, How does this work? Options

[nihil44]

I have bragged to my carburettored friends about how the '74 1.8 L Jet starts off the key even after a lay off of a month or so. Lately it has required two cranks to start. I suspected a vacuum leak as I pulled a plug and the pluf looks like the mixture is lean but the exhaust tips are black



I made a smoke maker based on this YouTube site

THE BEST SMOKE TESTER YOU CAN BUILD!! / THE MR. FUSION MINI BUILD - YouTube

Applied smoke into the intake system and this is what resulted.



Over the years I have read about ensuring the oil filler cap has a good O ring and cap seal otherwise unmeasured air will enter the intake system downstream from the Air Flow Meter and cause a disturbance in the A/F ratio determined by the ECU.

There is a factory hole in the oil filler cap as revealed by the smoke test. I have 2 filler caps and they both have the small hole.

How does this work if the L Jet intake system is supposed to be closed?

I was expecting the smoke test to reveal a vacuum leak in the intake boot or elsewhere and that would be the 'aha' moment. Not so lucky. However I would like to confirm that the intake system is vacuum leak free.

Would appreciate some explanation from the collective brain trust.

A word of caution: If doing a smoke test, perform it outside or in a well ventilated garage otherwise it will set off the smoke detectors. How would I know this?

David

[djway]

When I did my smoke test nothing came out that hole...

[wonkipop]

When I did my smoke test nothing came out that hole...

two possibilities
hole is meant to open.
or hole was gunked up?

mystery!

EDIT

there is a thread on the hole in the cap here. a lot of stuff.
samba.

https://www.thesamba.com/vw/forum/viewtopic...sc&start=20

i have not read it all. you got to sift through it to find the smart cookies.
its a bit confusing as they all talk between D jet and L jet.

obviously it is a vent though or it would not be there.

i took mine off again now that its nightime and shone a torch through it.
there is not light shining through the pinhole in mine.
does not mean anything. could vent in sideways or through a second layer behind it.