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

[Van B]

Alright my Ozzy friends,
I tested my oil cap today. I wrapped the side/throat (around the spring) in electrical tape real snug and put vacuum on the center bore using a rubber cup that came with my mighty vac. It was tricky to get the cup to sit well enough that I could pull vacuum, but once I got it, I was able to pull 25 in hg. It would leak down, but not faster than I could build vac. I think the leak was from the imperfect sealing. But regardless, the pinhole on top is definitely there to allow the diaphragm to move.
If I blew into it, no air came out the pinhole.
When you release vacuum, you will feel a small puff that is from the diaphragm spring pushing it back, but nothing else.

I guess I was imagining things when I thought I felt air coming through it…

[wonkipop]

Alright my Ozzy friends,
I tested my oil cap today. I wrapped the side/throat (around the spring) in electrical tape real snug and put vacuum on the center bore using a rubber cup that came with my mighty vac. It was tricky to get the cup to sit well enough that I could pull vacuum, but once I got it, I was able to pull 25 in hg. It would leak down, but not faster than I could build vac. I think the leak was from the imperfect sealing. But regardless, the pinhole on top is definitely there to allow the diaphragm to move.
If I blew into it, no air came out the pinhole.
When you release vacuum, you will feel a small puff that is from the diaphragm spring pushing it back, but nothing else.

I guess I was imagining things when I thought I felt air coming through it…

good stuff.

fair chance mine is ok too then.

been up country picking grapes at my uncles beef farm (with small vineyard).
took the big citroen.
my only problem was holding it under our ridiculous speed limits - 110 kph. (IMG:style_emoticons/default/sad.gif)
the cit just wants to run, 140-150. (IMG:style_emoticons/default/smile.gif)
almost as much fun to drive as the 914.......almost.
corners flat, no body roll - hydraulic suspension.
(there is one in the car chase in the film Ronin - takes a hammering getting rounded up by a big audi).

on way back today dropped in at workshop.

told mike about prv hidden in the oil cap.
he hadn't picked it either and he is a mechanic. he thought it would be down in the baffle somehow and hadn't bothered to look or think twice.
---said there is a mob in queensland he has in his contacts that repairs vacuum diaphram valves - if they have metal casings. eg, the decel valve i have found, if its not good.
but have to be metal vacuum valves.

however......if need be they may well have been a possible source for a new membrane.
we would just need to get (a potentially sacrificial) cap apart to explore the option.

------

@Emerygt350 sent me a pm with some photos of his fox body mustang he just had to break out and take for a spin in winter. i love it.
ford styling of that era is just right in my book.

(IMG:style_emoticons/default/beerchug.gif)

so.....here is some falcon shots for him.
its been keeping me away from pulling the 914 into the shop.
i'm nearly finished. got the prep and paint for the tub to go.
i have learnt body work on this poor victim.
replaced areas indicated in images. and anything painted black por15 in tub. which amounted to a lot of the car (in a key dicey structural area).
aussie cars do rust. did not get galvanised bodies until near the end of car manufacture here. this is a 94.
not going for over-restored with this one. its meant to go on as a functional work horse.
so we kept its lifetime accumulation of battle scars as much as we could and just went the rust. plenty of that!!! the interior is amazing. usually aus cars are like desert cars in usa - cracked dashboards, fried vinyl, brittle plastic hell. but this one has a showroom interior astonishingly. think it spent too much time parked under trees in the shade getting shat on by parrots which probably caused half the rust.

didn't do the paint. skills in that department extend as far as picking up a brush and applying Por15.