1974 620 need vacuum line schematic and routing

[Cardinal Grammeter]

Every single OE vacuum line has been stripped from my 620.

 

The FSM has some cartoons of some of them (carb, EGR, air cleaner, ...) but they are not accurate enough.

 

In particular, the pair of vacuum barbs on the base of the carb and the EGR.

[Leche]

On this page on the Datsun 620 section look for a file called "Emmision control system vacuum diagrams". Download the PDF file hopefully it has what you are looking for.

 

http://www.davidcmurphy.com/olddat/620tech.htm

[sebpv]

carpartsmanual.com

[Cardinal Grammeter]

Leche:  very impressive pdf, however mine is the bastard 1974 which is totally unique.  However, I can see some basic principles from your ref.  Another piece of the puzzle!

 

setpv:  I live in carpartsmanual.  While it is a great reference and a lot of help, its not enough

 

You'd think there would be a vacuum diagram just like the wiring diagram...

[sebpv]

how thorough do u wanna go with the vaccum lines. There are only a few that are vital: the advance line from the dizzy to the carb; the block breather to the intake, and the booster to the intake. The PO had already renoved 3/4 of the unecessary lines so I cleaned up the mess.

[sebpv]

The pump and the canister are not required unless "Californication". I went as far as removing the fumes tube from the gas tank to the intake. And to go even further, there are the pump relay connected to a bunch of stiff that then become irrelevent :)

[Cardinal Grammeter]

The 1974 does not have the air pump or canister (I think).

 

The EGR and EVAP stuff is unique.

 

Of course, then there is the question:  What was different in the CA version (was there one in 1974?)

 

If there is a CA version, I wonder how I could tell if I have it?  (Oh, there is an emissions dyno weight sticker on the firewall - I'm guessing that is for CA? - oh great, I have a CA?)

[sebpv]

Again, the question remains: what is your objective? Dealer stock, functional, Cali standards, etc...

[banzai510(hainz)]

Again, the question remains: what is your objective? Dealer stock, functional, Cali standards, etc...
 OCD!!!!!!!!!!!!

 

if he has stock carb and aircleaner then it matters a little bit

 

If weber 32/36 I say  carb to distributor the rest plug or pull out

 

I dont think has pwer brakes in 74 so worries there

[Cardinal Grammeter]

Stock air cleaner and Hitachi.  (frankly, that "splash of blue" of the OE air cleaner is iconic - will probably use one of the Pontiac engine paints to refinish it)

 

Trying to "put it back the way it was."    I know I won't get it perfect with exact tubing, routing etc. but since I have to plumb it, I'd like to get it as close as is reasonably possible.

 

The PB booster looks ancient like it was there OE.  The vacuum hose has a firewall bracket that looks OE.

[datzenmike]

There is no reason to assume this truck is California emissions equipped.

 

All 620s had power brake booster and dual master cylinders.

 

If you had an automatic there will be a very small vacuum line to the transmission joining the bower booster hose near the intake fitting.

 

Of the two vacuum line fittings on the valve cover side of the Hitachi carb, the front one is for the distributor vacuum advance. The rear one is for the EGR and can used or simply be left off to de-activate this emission device.

 

There should be a vacuum line to the air cleaner housing. Keep this operational for two reasons.

1/ This goes to a thermal vacuum valve that activates the vacuum motor in the air filter housing snorkel that mixes warmed air from  the hot exhaust with the cold air from the inlet. This provides an air supply that is kept within a close range of temperature and allows the engine to run better when cold. It also eliminates carb icing on extremely cold and damp days. It's gets both cold and damp in Pittsberg? yes?

2/ It is also connected to a thermal vacuum bleed to prevent an over rich mixture when idling hot.

[Cardinal Grammeter]

Thanks KingRat for the explanations - especially the side-by-side carb ones.

 

The emissions sticker on the firewall says it meets all Federal and California specs - so I guess it is a CA variant.   Oh Joy (sarcasm)

 

Haha, spent at least 4 hours taking the kink out of the fuel inlet fitting that was bent at the bend only to discover it is the "small one" and not the one the carb I'm using needs.  (I did use the one from the L20 carb - it had the large banjo.  Oh well.  Now if this used carb just works....)

[Cardinal Grammeter]

I'm in the thick of it now with the plumbing and have found help by looking in the parts manual for the vacuum hoses - the part number typically describes what they connect.  So that is a big help.

 

I know I've always slammed the 74 being that it was a "transition year" (but I really like to call it a bastard), but there is one thing sort of cool about it:  the polution crap was in its infancy.  It has a primitive EGR and a simplistic evaporative system.  The L20B, especially California versions, have the complexity of a nuclear power plant.  I would never attempt to restore that crap.

 

I have a pic of a L20B air cleaner with what appears to be OE vacuum lines still intact, but totally rotten, cracked and broken and am thinking maybe I should post a pic for reference purposes.  There doesn't seem to be much "historical" documentation out there. 

 

Maybe there should be an Official Thread for Historical Reference Pics, since it is quite rare to find something untouched.  Like that ex-Marine that had a 67 Corvette 390HP I think and when it approached 3000 miles, he stored it.  When it "surfaced" people from all over the world traveled to scrutinize and document it.
 

[Cardinal Grammeter]

...

 

There should be a vacuum line to the air cleaner housing. Keep this operational for two reasons.

1/ This goes to a thermal vacuum valve that activates the vacuum motor in the air filter housing snorkel that mixes warmed air from  the hot exhaust with the cold air from the inlet. This provides an air supply that is kept within a close range of temperature and allows the engine to run better when cold. It also eliminates carb icing on extremely cold and damp days. It's gets both cold and damp in Pittsberg? yes?

2/ It is also connected to a thermal vacuum bleed to prevent an over rich mixture when idling hot.

 

Finally am installing the air cleaner and yes, I thought there would be one vacuum line for the Temp Sensor and the Hot Idle Compensator, however each of those have their own vacuum line.  Those two lines are held in a little tab bracket wide by side in a direction that is "down to the carb/intake/engine." 

 

Delving into the FSM one final time, there is actually enough information to piece together what has to happen.  I have referenced all the Figures I used.  Aside from the bottom of the air cleaner, there are no pics of actual routing or where the T's are located.  There is some Holmes-ian information in the Parts manual where they identify the vacuum tubes' connections and their length in mm.

 

Turns out these two vacuum lines go directly to a T and then a single line goes to the engine (ET-35 Correct Position of Hoses) - I'm guessing the actual vacuum fitting on the Intake EGR Passage (Manifold) near the PCV.

 

I know the Evap Flow Guide Valve (under the master cylinder on the inner fender) does not have any vacuum signals.  Since part of this Topic (as per EF-22, 45 Flow GUide Valve, 47 Flow Guide Valve,) it has 3 lines that go to:

• the small nipple on the large crankcase PCV tube
• the air cleaner for clean air (there is a nipple on the air cleaner base for filtered air
•  the gas tank vent tube

The B.C.D.D. has a nipple that needs clean air from the air cleaner.  (EF-22 Sectional View of BCDD)

 

The clean air tube from the Air Cleaner goes to a T which splits it to the Flow Guide and the BCDD.

 

There are two T's in the circuit:

• FROM Air Cleaner fresh air TO BCDD and Flow Guide Valve
• FROM Air Cleaner  Temp Sensor and Hot Idle Compensator TO EGR Sub Manifold (i.e, "EGR Passage")

[datzenmike]

The hot idle and temp sensor just go to intake vacuum... anywhere will do.

 

The flow guide allows fumes from the gas tank to flow into the crank case (under certain conditions) to be stored when the engine is off. When running the PCV vacuums all the fumes out.

[Cardinal Grammeter]

I don't know if the Evap lines come under this topic. 

 

(I discovered today that they removed the Fuel Tank Reservoir that I believe is up in the wheel house.  What they did to the tank vents would make you cringe.  New thread?)

[datzenmike]

hope not....

 

 

... well condense it to fuel system. Anything fuel related. Electrical... anything electrical related. Like the Ratsun forums.

[Cardinal Grammeter]

Yeah, but the thread title says "vacuum" and the evap is not.

 

While I need to figure out what is correct for mine, the pressing problem is that the fuel gauge doesn't move.  It powers up to E but stays there.  Need to search fuel sending unit threads...

[abbylind]

Check the connection on the top of the fuel tank sender unit. Mine was corroded. Cleaned it up works great...

[Cardinal Grammeter]

I was taking some pics of my fuel filler hose I replaced and I think I can see the sending unit from inside the wheel well.  That will be on the list of things to do, but for now, I'm focusing on just getting insurance, plates, inspection, and on the road so I can replace the totally shot motor in my 91 Geo Metro 3-cyl (!)

[datzenmike]

If you missed my post.... If the gauge comes up slightly from below empty then the sender is probably covered in varnish from fuel evaporating while stored. If clean, the sender would rise higher but can't. Sorry, it might slowly work loose from gas sloshing around but it probably will have to come out. I had a sender from a 710 tank that looks like it was dipped into a can of varathane..

[Cardinal Grammeter]

Hummm...  wonder if one of those "removes varnish" additives might help over the long run?

 

Frankly, after I fixed the filler hose and put 4 gal in, I swear the gauge did not come up as high as it did when I had maybe 1-gal in it.  (It was a skosh above E before and a skosh below after.)

[datzenmike]

Well diosolved loosened varnish, if this is the problem, will have to go somewhere else like the fuel lines, pump and carb. I would take the tank out and clean it, if needed. Have several new filters and change then.

[Cardinal Grammeter]

I think anything that would dissolve the varnish would be a permanent solution - the only way to get varnish is for the gas to evap and leave it as a deposit?

 

I so do not want to remove the tank!  At least at this point.  I am so close to driving this 620 out of the car port!

 

(Actually, I have the seat back skin removed and fixing the broken spring and disintegrated burlap.  But that doesn't mean I can't put the bottom in and "drive it around" a little!)

________________________

 

But if I would get a reservoir tank and stuff (not even sure what is used in the 74), I might consider it.  But if the truck runs good w/o issue, I'd never be able to justify the time - this project was supposed to take a few months, not 1.7 years.