Don't give me too much credit. I have barely enough smarts to go & look it up in one of my workshop manuals first.

I was surprised to realise that this 1971 car had smog gear that we didn't get untill the B210 model. Our B110's use a fuel system unchanged since the 1930's

The pipe that you need will have just one fitting on it & that is probably common to quite a number of US 'A' series models, so with a bit of luck you can score a pre loved one from a donor engine..

If your engine doesn't have this small fitting, but the firewall does have the flow guide valve, then I presume it's not the original engine.

Why would some US models have the valve, yet some 1200 engines not have the fitting? Different smog laws in different states? Was California enacting harsher legislation than other states in '71?

Say Dodgeman, could I borrow that dunce cap from you. Looks like I need to go sit in the corner for a spell. After that I need to go look at my set up but I do have one question. The tube at the back of my block does not have the extra vaccum fitting coming off of it, what to do?

Edit: I think I just hijacked my first thread

disconnect the lines off the brake bleed nipples,just leave them dissconnected
tommo

Quote:
Why do you suggest connecting vacuum to this valve? Do you know what it does & how it works?
Didn't think so.

The device is called a flow guide valve & it controls the pressure inside the fuel tank & directs excess fuel vapour into the crankcase for temporary storage when the engine is not running.
Don't worry about the engine exploding from the fuel vapour in the crankcase, it's never happened yet with this system.

One line is connected to the fuel tank vapour separator & it has no valve in it so air or vapour can flow in both directions.
The lower one is connected to a fitting on the crankcase ventilation pipe at the back of the block.

The top fitting is connected to a fitting on the underside of the aircleaner.

When the engine is running, fuel is drawn from the tank which must be replaced by air. There is a one way valve in this flow guide valve that opens when the pressure inside the tank drops below a certain value.
Filtered air is drawn down the hose to the top fitting of the flow guide valve [it should have an arrow cast onto it pointing inwards to this guide valve]
This filtered air then flows into the tank & a pressure slightly below atmospheric is maintained.

When the vehicle is stationary, ... in the sun, pressure can build in the tank. When this happens the pressure in the line to the tank opens another one way valve in this wonderous device & the excess pressure, & fumes, are vented into the crankcase for temporary storage.
There should also be an arrow to indicate the flow direction on the lower fitting as well.

When the engine is started, manifold vacuum, via the Positive Crankcase Ventilation valve, draws the stored fumes from the crankcase into the manifold & they are burned before passing out the exhaust.

If vacuum is applied to the top fitting, nothing will happen as the one way valve allows flow into the valve, not out of it.
Lucky this time.

Anyway, we have now determined that this valve controls the pressure in the fuel tank, so your cap should be completely sealed I guess. It might pay to remove this valve & with a hand pump, perhaps a bicycle pump & some tube, test that it does all that it is supposed to do.
It wouldn't surprise me if the fitting with no hose, ... the one that is supposed to be connected to the air filter, is blocked. If it is, then you will end up with serious low pressure in the tank after a while.

They fit pretty well, I cant take credit for them since they were there when I got the car. I actually didnt even notice them my mail mail did when he was checking out my car lol.

Quote:

Datsunitis,
OK, looked at my car last night. Forgot there were two panels back there (age and crown royal are probably contributing factors). The one closest to the front of the car is access for the fuel sending unit and the on closest to the rear is the vent to the evapo unit. The vaccum valve in the engine bay is emission related. As Tommo said there should be vaccum lines attached to both of the forward pointing ports. On my car they are hooked into nipples on the right side of the brake master cylinder below the resevoirs. The other line I assume goes back to the evapo unit. Couldn't tell you how that works but that is the way my car is set up.
BTW...the bath tub stoppers for cylinder caps is brilliant. I've been wondering what to do about that as OEM caps are no longer available. Do they fit tight enough?
Kelmo

try adding vacume to top alloy fitting in photo
vacume opperated valve??
good luck
tommo

does it have a charchol canister?
thay shut of tank breathing when the car isnt running.
vacume from manifold opens valve on canister, or valve in breather line.
if it has anti pollution gear it wont breath out of cap.
sounds like u have vacume in tank,its like trying to get fuel to flow up hill??
take off cap see if that works.
are the lines on the pump the right way around????

tommo

its been a long time but im sure that 3 outlet fitting is a vapour separator and connected like that it isnst (separating vapour). does fuel flow through it to this point?
dazza
sorry we are all so vague but diagnosis is difficult getting info in small bites

this should be an easy prob to fix if you
1)examine entire fuel system layout
2)understand how it works
3)test system starting at one end and systematically working your way to the other
4)option! run carb gravity fed from fuel tin bypassing entire car system (eliminates carby)

expect your next post will be "guys! its fixed"
dazza

Here are the pictures, pardon the dirt have not had a chance to clean the rear. It did come from the northern Salt Flats of the mid west.

It does have the side evap system that you described.

The car was driven and serviced right before I bought it. It was not sitting very long. Tank was blasted and cleaned about 2 years ago at the tune of $250! I have the reciept. Also a new carb was installed (damn hitachi)