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Vacumm questions.


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I've been doing a bit of a truck update/thrash you know seats , head machined new head gasket set. Doing a thermostat swap today just because its cheap and why not. My searching on the interweb didn't return how much vacuum line I will need to go through and replace. Guess a lil' bit of a shout out to DatsunMike as he seems to know all this kinda stuff. (1986, Z24)

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So, quick tip for moving those restrictors over:


First off, there are three of them, and two sizes.  One with a larger opening, and two with smaller openings.  IIRC, the two smaller ones come off of the TVV, and the one larger one comes out of the carb base and goes to the EGR control line.  That all kind of makes sense, since those are the three controlled vacuum leaks in the system.



To remove: just use a sharp knife/razor to cut the old vacuum hose lengthwise down the side, and go easy when you're passing over the restrictors, as they're pretty soft (look like brass).  Make sure to clean them out with carb cleaner on both sides, and air-dry with compressed air if you got it.


To install: spray a little bit of WD-40 on the end of the new vacuum hose, then gently push the restrictor into the hose.  I either used my hands or a pair of needle-nose pliers.  After that, you need something long and skinny to actually seat it 1-2cm down from the hose end.  I used a roll pin punch of appropriate size and it worked out great.  You could probably also use a toothpick (the wood wouldn't damage the inner surfaces).

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The Delay Valves serve the purpose prevent sudden transient vacuum signals from triggering. These look like round discs in the vacuum line and were most common on vacuum advance and later with 3-port TVV EGR.


Restrictions in the line are used with vacuum-cut operations, so that when the vacuum line is opened it doesn't create but a tiny vacuum leak (not enough to affect the engine). The line is opened to allow the EGR diaphragm to move back. If they simply stopped the vacuum it would still stay on, so they had to let air in.

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The vacuum advance and EGR use ported vacuum not intake vacuum. It's only available above idle. When the throttle closes the vacuum line is open to atmospheric pressure again and drops by itself. You can remove either hose from the carb and leave open with zero effect on the engine idle.

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