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

[wonkipop]

@nihil44

i am looking at our cap and oil filler real close now.

and i'm wondering if its not pulsed in some way too. just like the VW engines.

can't quite figure it out yet.

but the whole cap sits down into one ledge and the breather hose joins above that.

more later if i can find something further on this.

need a cross section drawing.


point would be, if it is a pulsed valve incorporated into a screw down oil cap then if its blowing smoke out its failed.

this would kind of make sense.
the buses and the 412s had a separate oil filler cap and dipstick outside car for convenience.
so its just a pure pulsed crankcase valve on top.

but we have the oil filler cap and dipstick on top of engine.
is it a pulsed valve and screw on cap combined into one?

just can't quite fathom how it works looking at it just yet.

i can understand how the VW one works. but not this one yet.