If you're adding a return line for an electric fuel pump where the pump is at the rear of the car near the fuel tank, would it be better to add the return at the regulator at the front of the car that feeds the carbs, or put it directly after the fuel pump before the main feed line to the carb regulator?

Traditional(?) approach...

"Short line" approach right after pump...

For a street car in the heat, I like the return regulator as close to the carb as possible , a fuel log at the carb with the regulator on the end .

My car had the short line setup on it with a Mallory Comp 250 pump for years with no problems. A lot less plumbing with that setup. Comes right off the pump and into the tank....All in the trunk.

I don't know about now, but we had issues years ago with the return style regulators. You have to run a larger line for the return and need to be as little restriction as possible on the return line or you get into pressure issues.

I like the regulator in the engine bay for the same reason as Charlie, street car in the heat.

At low speeds on the street will be
bypassing a large amount of fuel. This is good for a real street car that is driven in hot weather,
because there is a cooling effect added by the constant movement of the fuel. But the extra plumbing
is a definite downside.

Either way can be made to work. If it was me I'd first try the regulator in the rear with a short return line. But, if you go that way you need to make sure that you have a fuel pressure gauge connected to the carb feed so you know what the carb is actually getting. There will be a pressure drop in that long line so you have to monitor the pressure at the carb inlet. And you need to pay attention to fuel line routing since a low pressure line will be sensitive to boiling.

EFI cars almost all put the regulator and pump inside the tank now and just use a single high pressure line up to the engine. But with 60 psi line pressure they don't have to worry about boiling. A carb has only 6 or 7 psi in the line so it can be disrupted with heat or even g forces from a hard launch.

Yep, ease of conversion vs overall effectiveness... I appreciate all the feedback.

Up front.

Keep it moving. Rather than lying there deadheaded against a regulator.

I used a lower budget way of regulating the fuel back to the tank. My thought was to keep the fuel moving at the carb, so my setup is shown below and my regulator is a .028" Holley jet in the return line up by the carb. It took a few jet sizes to get the final psi at the carb right, but the .028" worked out about 6.2psi at the carb and the rest of the fuel goes to the tank.

My car is EFI but it is plumbed with the regulator up front. Being a street car the recirculating fuel heats up pretty fast, it eventually gets all the fuel hot. My return fuel temp runs 120 degrees pretty easily and that is with running it through a cooler with a fan on it . Like Andy said a lot of EFI setups are starting to keep the regulator in the back to keep from returning hot fuel. I will eventually try that but have other items on the list first.

Couple of things to add, my car returns from the rails so that adds heat, I also didn't log temps before I added the fuel cooler so I really don't know how much it helps, it is back behind the stock fuel tank.

This. Here's my setup. Return regulator is the red Aeromotive regulator at the end of the log. -10 feed, -8 return. The return is plumbed into the stock 3/8" pickup tube. Pickup is from a sump in the tank.

I need to do some form of return system just to reduce the load on the Mallory 140 w/ the dead-head regulator. I remember that thing starting to sing the blues on occasion while stuck in summer traffic and would like to avoid repeating that scenario as much as possible.

The bypass should always be at the carb. Never back at the pump. If you put it at the pump, it takes much longer for the system to respond to the floats dropping. A short return line looks good on paper, but in practice it’s bad. And, think of all the fuel in the line from the pump to the carb. It’s still just sitting there, heat soaking. One last piece of advice. Buy a Mallory regulator. The one you have in the first post is just a sorry excuse for a bypass regulator. Running the fuel backward through a modified dead head regulator is not good. Use a dedicated bypass regulator.

Some fuel pumps bypass at a higher than optimal carburetor pressure directly at the pump to keep the pump cooler. The bypass regulator up front also bypasses fuel, but at a much lower volume than the fuel pump is bypassing. I ran my fuel system like that for years at the recommendation of a fuel systems engineer.

I'm looking at RobbMc's regulator to go along with his 1/2" sending unit that includes a return feed. https://www.robbmcperformance.com/products/regulator_bp.html

The RobbMc unit should work. I've had good luck using Robb's stuff over the years. Have you decided where you're going to mount it yet? Front or rear? The big difference is the extra length of hose that you have to run.

Front

FWIW I tried a return system on my street car, ie pump gas car thats not used alot. After having to replace the return line for what would have been the third time, in 8 years I decided to NOT use the return regulator and line(mounted near carb) and just use the pump bypass. No ill affects, no issues in traffic in Vegas heat and no difference at the track, been like this for 14 years. Pump has been in the car for 22 years....Never had to touch it.

What was going wrong with the return line?

Same here, pumps been on the car since the 90s.

If I went back to a carb I would run the single line to the carb and let it eat.