Datsun Roadster Forum-311s.org

This question concerns the device atop the rear carb float bowl on 68 1600 that allows for recycling to fuel tank unused gas. In the attached drawing it is the item closest to "FOR USA". If I can't blow through this fitting when the float needle valve is closed, could that be a reason for the rear carb always running to rich? The reed in this fitting has it's own needle valve. What if I removed the needle valve or does it have a necessary use? Thanks for any responses.

Leave it as is. It also functions as a basic pressure regulator. If you remove the internal valve and leave the return path connected, your fuel pressure will drop to about one psi (or less) and starve the carburetors. (The fuel will take the path of least resistance, which is back to the tank).

You can block off the fuel return- early cars had no return- but depending on your operating temperature, you may run into vapor lock problems. The main reason to recirculate the fuel is to keep it cool.

Like he said!
Trust me you don't want to get vapor lock issues
Mind you, it does depend on your local climate: our hot summers here in South Australia caused my car a ton of fuel problems until I insulated all the rigid lines in the engine bay

Thank you both for settling this multi-decade question about that reed valve.