Hello Teeners! Is there anyone can share any pictures how they do a return fuel line especially on the carb side?
Since I will be replacing my fuel lines to SS and removing my fuel tank to clean, much as well prep everything with return line.

I have Weber 36 Idf with 32vent

Thank you!

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I have never ran a return line with a carb setup, but have heard of guys that have. My thought is why complicate things?

There is a diagram showing multiple ways to plumb this
I know I’ve posted it in a dozen threads
I’ll look for one

A return line is best.
What the factory did
Cooler fuel
Less vapor lock
And theoretically more hp
Brant

Here

I’m using B

E is a match to how the factory plumbed the DJet system

I have mine set up in the stock configuration using a stock (EFI) fuel pump. Works great. Another advantage of running a return line is that the fuel tank was designed for a return line to keep the reserve fuel bowl full. Without the return line, you are likely to start sucking air before the reserve fuel is depleted.

Good to know, I have no return, will be aware to have always gas…
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I also installed “AN fittings” (CB performance)

Near as I can tell, the reserve bowl full keeps the last bit of fuel from sloshing around in corners to keep the pickup tube submerged. I'm guessing keeping the g-forces down would also get the last bit of gas to the carbs.

Unless the tanks differ, the part in the center is a baffle, not a reservoir (note the holes in the side).

Further, the tank pulls (finger filter) and returns (the other hole) within this baffle.

This photo was a result of my pouring in some Stabil without ensuring the paper disc was removed from the mouth of the bottle. I was quite unpleased (I got it out with a flexible grabber).
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I tried but ran into issues with the small return pipe and the pressure of the FI fuel pump with a PMO regulator. The FI pump was making 5-6psi just with the return line restriction making it impossible to get the 3-4 psi for the carbs. The solution would be to run a larger return line. FYI a larger return tube is recommended for a return system, I think the small OE tube is fine for FI, only low pressure carbs run into this issue.
Another possible solution was to run a Holley V8 pump that runs at 7-10lbs.

At this time I was trying to get my teen running for a show, so I slapped a low pressure pump on (that I had) with no return and it's been that way ever since.

I have always used the Holley pressure regulator (1 in, 2 outs) that has no return line for my early buses that have the single outlet tank. For the 914 I’ve been working on I think the best plan is to replace the fuel lines with the stainless equivalent of the stock lines (early with the pump at rear) and use the Holley regulator that has the return line (1 in, 1 out, 1 return).

Remember OP said carbs. This is a 50/50 6 hour argument topic. I have seen compelling info from prominent people on both sides.

One question I have is that most setups go from the filter/pump straight to the 3/4 carbs and then to the 1/2 carbs. Doesn't that just give the 1/2 carbs what is left over from the 3/4 carbs? Wouldn't a Tee to the feed side of the carbs be beneficial and then a return from the 1/2 carbs if you want to? Would be interesting to see fuel pressures on both sides of that single feed line.

The Webers (and Dells) do not offer an in/out port. Therefore, it will be "teed" outside the carbs.

I was also curious about what Mark offered: where did you find a pressure regulator that will knock the stock EFI pump down to 3-4 psi? I'd suggest much more system pressure than that and you risking over-riding the float/needle valve.

I run single-line on the race car with Dells.

I just went through an exercise on my 2.7L six (with dual Webers). Yes, some of my issues were self induced. Some of the issue is trying to introduce non-OEM parts to make fit for a custom application.

Some of this can be considered a Public Service Announcement on what not to do (previously covered in a recent thread).

In theory, I believe that a recirc coming from a pressure regulator (return to the fuel tank) and close to the carbs, with a tee to feed both carbs would be the best solution to maintain constant pressure and the added benefits to theoretical fuel temp/fuel pump longevity.

I wound up trying three different electric fuel pumps (no recirc) while I was learning what would work for me. The first was a low pressure, low flow (Delphi) that fed into an Aeromotive 13222 regulator. The regulator was located on the rear firewall close to the carbs. The guage at the regulator indicated a constant supply pressure of a little less than 3 psi (after tuning).

During sustained higher RPM loads (freeway driving), the car did experience what I felt was slight fuel starvation. Obviously, my first pump was undersized for flow.

I had already eliminated the recirc line from the tunnel/fuel tank. I still had the parts to return to that option, but, sought a non-recirc solution. I had also initially constrained myself to trying to find a fuel pump that would fit under the steering rack...I wanted to keep any potential fuel leak out of the car. That decision obviously limited my fuel pump choices. My percieved choices of fuel pump were also limited as I wanted to maintain a 3/8"/10 mm fuel supply system from the tank through to the rear.

I upgraded my initial Delphi pump to another (what was advertised) as a low pressure, higher volume (Walbro) inline electric pump. The second pump worked for me for about 8-9 months with the same, non-recirc, pressure regulated set-up.

One day (just within the last few weeks), the (secondary) plastic fuel filter I had installed ahead of the regulator ruptured...I knew that the newest pump was pushing about 12 psi to the regulator. Never expected the fuel filter to fail as it did. I got lucky! No resultant fire as I was there at the time and saw the massive fuel "lake" forming under my car at the time of failure.

I retrofitted my forward fuel pump location (inside the frunk) to accommodate the Carter rotary vane pump. This pump is designed to be used with or without a recirc and is advertised for a maximum, internally regulated 4 psi.

The issue I found with the Carter is that it would no longer work with my Aeromotive 13222 regulator...could never achieve more than about 2 psi (and it would drop off to almost nothing under load).

Bypassing the regulator, the Carter pump was pushing close to 5 psi to the Webers. (Verified with 3 different fuel gauges I had available.)

I swapped the Aeromotive regulator with a billet aluminum Nitrous NX 15952 regulator. A non-recirc model that was advertised to reduce pressure in a range between 1.5 - 11 psi. Turns out that regulator was not as advertised and would not reduce pressure to the carbs below 4.5 psi.

I then bought a cheap, over the counter regulator (Spectre) from my local Autozone to test...installed it and the pressure regulator would not respond to adjustment. Perhaps that Spectre was just a faulty regulator. Despite the Spectre regulator looking like a Chinese knock-ff of the Holley 12-804, I reluctantly purchased and installed an official Holley regulator as my last step.

The Holley regulator was able to reduce the pressure from the Carter pump to just below 3 psi.

So far (about 3 weeks now with this current set-up), I have not experienced any issues (neither pressure nor high speed starvation). No issues with vapor lock either considering my south Lousiana climate.

Long story short...based on my experience...you'll need to consider a "systems approach" to whatever you plan on doing. In hindsight, I would still consider a recirc from a (capable) regulator back to the tank if my recirc system was still viable. (My current set-up still shows about less than 1/4 psi outlet variation between idle and high load without a recirc.) The conterweighing opinion is the complexity of a recirc from the engine bay back to the tank (as was the OEM design with my original FI 1.7L with the fuel pump/filter located under the right side bay area).

There are alot of options/opinions out there on what path to take. (I'm sharing my initial experiences only as a guide, and in some instances, as a guide on what not to do!)

One thing I did notice with the Carter pump, is that it is not a "constant positive pressure" pump once the power is shut off to it...fuel pressure at the carbs immediately bleeds off at loss of power to the pump...this could make a huge difference in the event of an engine bay fire (and my immediate future plans of adding an in bay fire suppression system, such as the BlazeCut).

I vote for option D.
With a pmo style regulator.

That's the combo I've been using for over 15 years, and it's never failed. The Carter pump being rotary vane is high volume low pressure. They say you don't need a regulator, but it is about 5psi iirc, so it's advisable to regulate it. I run it at 3.5 psi.

Looking at the regulators at Holley, the non return one that I use specs at 1– 4 psi, but every bypass option is 4–9 or 4.5–9 or higher which I think is high but maybe would work. I use viton tipped needle valves in my Dells.

It seems like the return line might complicate the system to make fine tuning at the pressures these carbs like to see more difficult. I'm rethinking, going toward not using the return line — install it in case I want to reverse that decision but cap off the inlet at the tank. Unless there is another regulator option, one with a bypass that allows for adjustment in a lower range?

PMO sells the this regulator for their carbs, stating that it will work with a stock 911 FI or CIS pump. This regulator is designed with a return port, in/out and two carb ports one for each carb. Not sure but I'm thinking the 911 has a larger fuel return line. In my 914 I couldn't get the pressure lower than 7 lbs at the carbs.

In my case I had no need for the regulator, I installed a redline fuel pump, good for 3 pounds of pressure. Its a tiny pink pump. No fuel return. Works fine, on my dual 44mm carb setup, I don’t know on a 6 cil, will need more, maybe yes.

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I see various specs on that pump, some say 3–4 psi, some say 3–6 psi. Seems it is lower pressure than the Carter 4070 I have been using though. I think the range of pressure in the spec maybe is to do with the size of your lines. Currently I have 3/8" throughout so on the big side. I even machined a 3/8 fuel tank outlet to have no bottle necks. Could be a good option.

Thank you everyone for all the responses!

Ok I'm an idiot what is the key to the diagrams ( the circle the rectangle and the square with the triangle)

Yes, it is a very well engineered reservoir. The pump is constantly scavenging fuel from inside the reservoir and dumping it back in which will serve to keep the supply line submerged. The holes are needed to allow the full tank to be used. Without them, the supply line would start sucking air as soon as the fuel dropped below the lip of the bowl. I've actually watched mine with a low tank and pump running and it does indeed keep the level inside the bowl higher than outside. Don't know if it still works with low pressure carb pumps since it depends on return fuel being added faster than it drains through the holes.

1. Big Rectangle : fuel tank
2. Small rectangle : fuel filter
3. small round : fuel pump
4. pentagon shape : fuel regulator
5. then Carbs

I think that is what I understand.

Thanks makes sense now . I'll try B. My regulator does not have a return port

I'm running this Malpassi bypass regulator. So far it has worked perfectly holding the pressure at the carb at a steady 3.5 psi. It has been so steady, that I finally pulled the pressure gauge after monitoring pressure for 3K miles without seeing any variation in pressure at all. I'm running SS lines.

The important key is using a bypass regulator that bleeds off enough volume of fuel from the supply to maintain pressure rather than choke down pressure like in a typical dead end regulator. I almost went the PMO route because it is supposed to do the same thing, but now glad I didn't after reading Mark's post.

Are you using the "boost reference" port or just plug it and it works as just a regulator with a bypass?

Same question for @BBrock and which configuration are you using?

My configuration is:

1. Tank
2. Filter
3. Pump
4. Bypass regulator
5. Low pressure regulator
6. Carbs

I have a Holley Blue high-volume pump followed by this bypass regulator:
https://www.holley.com/products/fuel_system.../parts/12-803BP
The bypass ranges between 4-9 psi which is too high for my Webers so I have a low pressure regulator in the engine compartment. I'm using this one:
https://www.holley.com/products/fuel_system...rs/parts/12-804
My bypass line is in the frunk and dumps into the tank. This was to keep cool fuel flowing through the high-volume pump which would get hot during idle or low flow part throttle settings.
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I just left the "boost reference" port open. I believe that is what the instructions specified if it wasn't being used. And yes, it works just as a bypass regulator in that configuration.



I believe I'm using option C, but it might be D with a Tee just after the regulator output. I'll check tomorrow and confirm.

Forgot to check yesterday but I'm using option D. I like C better but didn't have the fitting to run through the 3-4 carb so I could eliminate the Tee (actually a wye in my case).