Fuel return line?
 

Hi guys....appreciate the help on my previous posts...

I am in the middle of a frame off type rebuild of a 68 bird. Engine is now assembled, rear clip is back home (primed) and i now need to put it all back together. I will be replacing all components of the original fuel system...tank, sender, lines, pump. The car has AC, and had a return line, engine is a 400. Do i need to continue to have the return line? Is there an advantage to having the return line? I will be going back with a stock pump and quadrajet, and using stainless lines. The return line costs another $100 or so, and i would just as soon not buy it if i do not have to.

By the way, has any one tried In-line Tube for their lines? Classic, NPD or Year One sells them also, but I thought In-Line might be better. Also getting brake lines. Thansk in advance.

The small return line allows a small amount of fuel to return to the tank to keep the fuel circulating and help prevent vapor lock. It is needed most during hot weather, with the A/C running and with the car at idle or low speeds.

Pumps designed to use the return line also have a stiffer spring above the diaphragm than pumps designed for use without the return line. This is done to compensate for the pressure drop caused by the fuel returning to the tank.

You do not absolutely have to run a return line. However, keep in mind that you are more likely to have vapor lock in hot weather. Also, you may need a fuel pump designed to run without a return line (ask for one for a car without A/C) because if you simply plug the return port on the pump, the pressure may be too high and flood the carb (especially a Q-jet; Holley carbs can usually handle the increase in pressure).

I'll second robbmc's reply. I just got done diagnosing the same issue he mentioned. I had a pump with a return line blocked off and it flooded my Holley. I have a correct pump coming amd am sure this will fix my problem.

Get the correct pump for the correct set up.

The early sixties big cars (at least) took care of the return fuel line with a gas filter that has the return line and not by a fuel pump. I just picked up that filter from NAPA. I have a '64 GP with air and stock it has a return line fuel filter.

If you are running headers or making above average H.P. and live in a area that is warm a return line is real nice to have. I had vapor lock issues on hot days in the past running a mechanical pump with no return. No problems whatsoever now with an electric pump and a retun line. Fuel just circulates to keep cool.

Thank you all. I'll go with the return line set up.

Thank you all. I'll go with the return line set up.

Good choice. When I look under the hood and don't see the 3/8 main feed and the return line I always assume it to be a clone. Remember the dual line sender comes with a 3/8 inlet.

I'm back....as stated before, i decided to stick with the return line setup. I ordered a new fuel pump, listed for a 1968 400 4bbl. The pump I received is a new AC Delco Part No. 40607, and looks fine, except for one thing. The nipple to attach the return line to is closed off on the end, except for a pinhole at the center. The old pump I am comparing to has the nipple opened up to about 3/16", similar to the incoming fuel nipple, but smaller diameter. Old pump is an AC #52 40607. The old pump came on the motor I am rebuilding, which is a 68 400 2bbl from a Catalina with AC.
Can I use the new pump I received and still get the benefits of the return line, or do I need a pump with the fully opened return nipple?
Is this return nipple for a 'fuel vapor return line', and if so is there a difference between that and a 'fuel return line'?

Thanks in advance for any help you can give me.