carb to tank?

[Toronado]

Hi, I have two lines from my gas tank,
one feeds the carb and the other goes back to the tank.
Does the return line cycle the gas?
If so why is it a smaller hose?

Thanks.

[Schurkey]

Hi, I have two lines from my gas tank,
one feeds the carb and the other goes back to the tank.
Does the return line cycle the gas?
If so why is it a smaller hose?

Thanks.

Typically 5/16 or 3/8 tube supplies the inlet of the fuel pump.  The 1/4" vapor return tube does allow liquid fuel to return to the tank, but there's an internal restriction in the fuel pump (perhaps .060) that dramatically reduces the volume of fuel that can escape down the return tube.  The PRIMARY purpose is to bleed off fuel VAPOR, and therefore reduce vapor lock problems due to high underhood temperatures caused by big engines in small engine compartments, and high heat load from air conditioning.

Used to be common to have a non-vapor-return system on cars without A/C, and the same vehicle optioned with A/C got the vapor return tube, the extra fitting on the fuel pump, and the extra fitting on the fuel tank sending unit.

The vapor return system is very different conceptually from what the hot-rodders use when installing a return-style fuel pressure regulator.

[Toronado]

Very interesting, & informative.
thank you.

I wonder if since my A/C is removed, I can
remove the vapor return line? If it was just
for the A/C setup.

[Schurkey]

Very interesting, & informative.
thank you.

I wonder if since my A/C is removed, I can
remove the vapor return line? If it was just
for the A/C setup.

You could, but you'd be going backwards in terms of sophistication.  You'll gain nothing but extra expense from buying parts that don't improve performance or reliability; and could potentially cause vapor lock problems in hot weather.

Removing the vapor return system is kinda pointless.  I try to ADD it to my vehicles that don't have it.

[Toronado]

good to know, my lines are going to be replaced
from the pump to the tank, so had to put it in perspective.
My rubber hoses look dam near 40 yrs old, it bad.