The Gas Tank has to be vented to allow air to escape as liquid gasoline is pumped in, otherwise an air pocket would form at the top of the tank and prevent the tank from filling completely. Note that the Filler Neck enters the tank well below the top of the tank. Air also has to be drawn into the tank as the fuel is pumped out to prevent a vacuum from forming in the tank.
Pictured Below: 1969 Production Z without GVRS. Note that the “T” fitting in this case points UP to allow the Vent Line to be routed up above the Filler Neck. This allows only Vapors to escape - no liquid. It also allows Air to be drawn in.
(Pictures by Mark Bradberry)
Pictured Below: Factory Gas Tank used with NO GVRS. Note that the only tank vent is at the top of the tank.
Now lets look at the Factory Setup with all the GVRS hoses and the Gasoline Vapor Recovery Tank installed (diagram below). You can see that this Tank has additional Vents - one on the lower Driver Side and another on the Top Front Passenger Side.
Also NOTE that the tank vent on the top Rear Passenger Side (near #13) is shown pointing toward the passenger side in the diagram; in fact it points toward the Driver Side. The Factory used a pre-formed hose with a 180 degree bend molded in. Using aftermarket fuel line as a replacement, you will have to make a 180 degree fitting or protect the the bend in the fuel line - that prevents the line from kinking and shutting of the air flow. More later - but be aware of this from the beginning.
Pictured Below: Factory Diagram and then a picture of the actual tank.
Pictured Below: Factory Fuel Tank with GVRS additional vents. To use this tank you have to Cap Off the two additional vents. 14mm -1/2 in. and the 10mm-3/16 in. shown. So you will only be using the 17mm-5/8’s in. line.
Pictured Below: Finally This Is How Your Replacement Vent Lines Are Routed.
Or you can use an E-Z Coil aka UniCoil to make the necessary bend. Google it - make sure you order the right size for the hose you are using.
You can use a copper pipe cap of the correct size, filled with J-B Weld, to cap off the unused tank vents.