Fuel system ventilation

[fiveoneO]

I'm currently working on a 69 510 wagon. This is the first 69 wagon I've worked on and it doesn't have a charcoal canister or any other way I see for the fuel system to vent. Did these come with a venting gas cap or is there some other way the fuel system was able to breath?

[ggzilla]

Charcoal canisters came in 1975

1968-1969 the tank vented back by the fuel filler tube, with a hose down to the ground

From 1970 to 1974 Datsuns had the tank vented to the engine compartment to the Flow Guide Valve and then to the air cleaner and intake manifold. Finally, cars stopped smelling like raw fuel

[datzenmike]

It is actually vented through the flow guide valve which allows fuel tank vapors to push out the tank vent line through a one way valve and into the crankcase of the engine for storage when engine is off. When the engine is started the PCV valve draws any stored fumes out of the crankcase vent and into the intake manifold, into the combustion chamber where they are burned. The flow guide valve also has a hose from the air filter that allows filtered air to be sucked back the fuel tank, again through another one way valve as the level lowers from use. The 510 gas cap must not be a vented type for this to work and prevent hydrocarbons escaping into the atmosphere.

 

 

On the 510 it's located above the steering box, below the clutch and brake master cylinders on the inner fender sheet metal.

[ggzilla]

FUEL FILLER CAP are all non-vented

 

* 1968-1979 Nissan 17251-22904 non-vented cap

* 1970-1972 Nissan 17251-N1120 non-vented cap (with vacuum relief)

 

Early type: plain. Late type: with vacuum relief nubbin

[fiveoneO]

2 hours ago, ggzilla said:

1968-1969 the tank vented back by the fuel filler tube, with a hose down to the ground

Is this also true for the wagon? I had a 69 sedan once and this is how it worked, but this wagon doesn't have any way to do that.

[fiveoneO]

@datzenmike My car doesn't have that Flow Guide Valve. I guess it could have been removed at some point, but the third hard line it attaches to isn't there and there isn't any place to attach that line to the tank.

[datzenmike]

I don't think all 510s had the evaporative control. All with evaporative control had the non vented gas cap 17251-A5900. If not equipped a vented gas cap 17251-22094. 

 

Gas caps can be switched but yours should then have a vented gas cap. If you don't have a vented gas cap the fuel pump will have a hard time emptying the tank. If, when you take gas cap off to gas up, there is a whoosh of air into the tank this is why.

[ggzilla]

1968 and 1969 models were pre-EVAPO

 

Both fuel filler caps are non-vented. The newer cap has a vacuum relief, but it does not vent pressure from the tank, instead tank vents through the vent hose