The overflow fittings should have hoses that direct any spilled gas AWAY from the hot exhaust manifold. Remember they are only there in case the float should stick or sink and the carb over fill. This may never happen, but you want to keep gas and hot manifold separate.
Converted_to_datsun wrote:A return is for excess pressure, those vents are in case of overflow. Wouldn't work properly
The return line is not there for excess pressure. The L fuel pump is regulated at (about) 3 to 3.5 PSI. L20Bs tend to run hotter under the hood than earlier Ls. This can cause the gas in the fuel line to the carb, and the gas in the carb to boil. This is particularly bad when the motor is shut off in hot weather. Under hood temps soar to 200F or more and the gas in the lines will boil. Vapor in the hot lines prevents gas from flowing into the carb and the gas in the carb has boiled away.. starting is difficult to impossible. To reduce this, a return line is added and cool fuel is constantly circulated past the carb and returned to the tank.
Now simply adding a return line won't work, as there is no reason for the fuel to push past the needle valve and into the carb when there is an open easier path back to the fuel tank. To increase the pressure on the carb side a restriction is placed in the return line. The fuel pump pushes fuel against this tiny pin hole and pressure builds and now is enough to force it's way into the carb normally.
Return lines are a great idea on any car as the fuel in the tank is constantly recirculated through the fuel filter. Think about this... dirt and rust do not accumulate in the tank. The filer collects dirt all the time and keeps the tank cleaner.
Restriction at the tank end of the hard line above the fuel pump.
please feel free to like this post.My Datsuns, like good friends, have never let me down. At least in any way that was not understandable and thus fixable.
