1975 280z Fuel Tank Venting

[NC280z]

Good evening everyone,

 

I'm doing a refresh of the fuel system to my '75 280z (changed the topic of the original post to suit), and I've got a quick question regarding the vent lines on the expansion tank and the outlets on the fuel tank. It looks like the '75 model year was an oddball for differences between the fuel tank and expansion tank, as the fuel tank has 3 vent tubes but the expansion tank only has connections for 2 vents, plus the line that runs up front to the evap canister and a line to the fuel-filler neck. The main difference is that the '75 and older fuel tanks have a 1/2" vent tube right near the exhaust that was removed (probably for obvious reasons) in later model years and it does not have a mate of similar inlet diameter on the expansion tank. If I keep the topmost vent lines ran to the expansion tank, would it be alright to just cap off the 1/2" vent tube? What would you all recommend to cap the tube? The previous owner had a mishmash of adapters and tubes to run the 1/2" vent tube to the expansion tank, but left the 3/8" vent tube open to atmosphere which I believe has led to moisture in my fuel and a rapid degradation of the fuel itself. Tank photo borrowed from another Z site, as below: 

 

Edited April 19, 2020 by NC280z

[Stoffregen Motorsports]

Not specific to the 280Z, but I have encountered problems when capping off any tank vents. They are usually strategically placed to allow for fuel to move around without causing air pockets. I had a client once complain that fuel would shoot out at him when he filled it up. It was an aftermarket tank without vents. We installed the vents in the factory locations and the problem went away.

 

I did find this diagram on another forum. Maybe it will help.

[NC280z]

That helped, thanks! I ended up purchasing a 260z expansion tank, as it's made of metal (early 240z are plastic) and it had all the requisite vent inlets. It's very odd that the stock '75 setup didn't have all the correct inlets, I'm not certain what the stock setup would have done to ensure proper tank venting with all the extra outlets.