Datsun fuel line size

[hdjuyt5]

Hey, on your Datsun which is larger diameter.... the fuel line from the tank, or the return line to the tank?????

 

Only '75 and up L20B engines had the return line. Not sure abour A series. Include EFI engines as well with rear pumps.

[datzenmike]

I'd say for carburetor, the return is never smaller. It can be the same as the supply, or larger. 

[ggzilla]

A-series fuel return line debuted 1975 USA models and 1990 JAPAN models. As I remember it was the same size as the fuel line: 8mm

 

Here's what the Nissan publication "Introduction of Datsun B210 (1975 model)" says:

Fuel return system

 

For preventing abnormal fuel temperature rise, the fuel return system has been installed. In this system, fuel from the fuel tank is delivered to both the carburetor and fuel tank.

 

The fuel return line services to return a part of the fuel to the fuel tank to suit different engine operating requirements, preventing the possibility of fuel heated flowing through the fuel line inside the engine compartment, and elminating "percolation" inside the carburetor.

Thus the return line prevents vapor lockᵂ (engine stalling and engine hot-starting issues)

[fiveoneO]

Typically the return line is a larger diameter. They don't want any kind of restriction. Restrictions can cause fuel pressure to increase.

[ggzilla]

Typically for fuel injection perhaps. But for keeping the fuel circulating to avoid heat soak, the Datsun return line is same size from what I've seen. There is no restriction compared to the feed line. The pressure is regulated at the fuel pump

 

@datzenmike, doesn't the 620 return line have a built-in restriction?

[datzenmike]

It sure does. A pin hole just before entering the return line. If there wasn't a restriction the fuel would just flow back into the tank and there would be no pressure to push past the needle valve and enter the fuel bowl. Another benefit is the fuel is constantly filtered.