I know @MarkHenry has talked about this but I want to also do this and have a few questions..

I need to buy my stainless lines for my car and my question is that I have a PMO regulator that has a return to the tank and am using Webers on my -6.. Should I be running all 4 lines from Tangerine or is there another better option?? I want this system safe..

I am doing the same setup, PMO regulator and new tunnel lines from Tangerine Racing with the large supply line & small return. I am going to do regular (ethanol/FI) fuel line in the engine compartment to the regulator and fuel filter canister.

Ben,
Just curious....if carbs typically require 3 to 4 or so lbs. of pressure, are you talking about running higher pressure and letting the reg. return anything higher than required to the tank? I know you do this on a fuel inj. system, but what's the advantage to doing this with carbs?

I got this 10 micron filter from Summit and ordered a spool of the smaller sized line. Will need to get the larger size line for the supply and work out the fittings.

The advantage is cooler fuel.. Less vapor locking..

How did the factory -6 use the return?

Yes, you can run a FI fuel pump and will return the excess pressure to the tank. Fuel should stay cooler I guess. The better carb pumps run 7-12lbs from what I read, so it would need a regulator and return as well.

http://www.914world.com/bbs2/index.php?showtopic=269922

914-6 stock fuel system discussion.

Edit: from the pic below you see that the return is right at the pump, which will be different from you pmo regulator. I would buy the 4 piece kit from Tangerine, with the 2 short lines that penetrate the engine shelf. I bought the 3 piece 914-6 kit and didn't think it through.

I would definitely recycle the fuel to keep it cool

@TravisNeff that's what I was thinking.

Well I'm just running a -4 but am doing the same for my carbs. I just ordered a line kit from @Rotary'14 a couple days ago. I haven't decided on my pump and regulator yet but keeping all of the lines stock diameter and will fit with ethanol FI hoses. In addition to keeping the fuel cooler, the pump doesn't work as hard with a return line. Bonus for me is that if I ever decide to put the stock FI back on, I won't have to mess with the fuel lines again.

I took another approach and moved a Pierburg low pressure pump up front by the steering rack, and then simply ran the one fuel line back to theeng8ne compartment. As the fuel in the line is already pressurized, it’s less likely to vaporlock. However, I don’t see any downside to running a return line back to the tank.

I was running a PMO "regulator" on my 3.0 carbed 6 with a return line. It seemed to have worked for a while, but then I realized my pressure on the gauge was anywhere from 3 to 9 psi. No amount of adjusting would drop it to stay consistently desired range. The PMO unit is not really a regulator. No spring. It is more of a flow restrictor. I ended up using a Holly low pressure regulator with no return line.

What pump were you using and what pressure was it rated to put out?

Jeff B

The ideal is the OEM Bosch 3 port fuel pump (009) moved to the front.
They are very expensive. I must admit I haven't done it on my original 6
It can be slow to hot start.
In my conversion I'm running a Pierburg up front with just a supply to the carbs.
No regulator but a discrete fuel pressure gauge.
I've done the PMO anti-percolation mod to the Webers and added heat insulators
below the intake manifolds.
Fingers crossed.

I have a mallory 110 that is rated for 7psi.

I have been using a Holley Red 7psi pump with no return line or regulator and this setup has worked great for over a decade. It had a regulator at first but one or more of my mechanics/builders deemed it unnecessary for this car, which spends most of its time near or at WOT and at high-RPM, chugging fuel like there's no tomorrow. Maybe I will reinstall the reg and think about a return line if I put it back to streetable configuration.

There's primarily two types of pressure regulators, blocking and bypass. Blocking you put before the carbs, and bypass goes after the carbs with a return line.

I generally follow the strategy of "keep it simple". I have carbs on my 2.7 911 engine, with a low pressure fuel pump up front (Tangerine), pumping to a pressure regulator located just before the carbs, maintaining 3 lbs. pressure, with no return line. I have no fuel delivery problems.

a return line produces cooler fuel and should produce more HP (ever so slightly)
all modern cars use a return line and even the factory used a return line

The return line keeps your fuel cool and cools down and reduces load on the fuel pump. Keep it.

my vote D

Don’t have a return line, using option A with a pressure gauge where the black dot is. Seems to work fine on my Weber curbed six. It is not easy getting quality gauges and low pressure regulators. There is a lot of crap out there.

If I were to have a return line, it seems Option B with a gauge makes most sense to me.

Option B won't work, in that case a reg needs to be on the return side of the circuit or it will never build pressure.
BTDT

I did D as well.

A with a blocking regulator, or E with a bypass

Filter before or after the pump, or does it not matter?

Before the pump, I have option D I have a filter before the pump and a filter on each carb feed hose. So I have 3 filters, tank screen and each carb has a screen filter to keep the nasties out.

OK, I have that big canister filter and was looking at it yesterday. To take it apart to change the filter it needs to be mounted pretty high to get that cup off the bottom past the filter. I was thinking about putting that filter on the frame rail in the engine compartment,where an OE pump would go. I'll still use a small filter before the pump. Sounds like it would be ok

Three filters, one before the pump and two at each carb

I think from the diagram you have options O, C & D

Couple questions:
1) I think Mark mentioned this on other threads, but with a bypass regulator and return line, you should be able to run the stock FI pump on a /4, correct? What are the pros and cons of running a higher pressure pump with a bypass? One advantage for me is one less thing to buy but wondering about performance, reliability, and longevity.

2) What is the advantage of D over C? C looks to be the stock setup with allowance for a relocated pump. Just curious.

I would imagine that D over C would be good due to potential pressure drop after passing through the first carb

A pump is just a pump, it doesn't build pressure, that's the regulators job. Put a FI pump on with no regulator and it won't build any pressure, lots of flow, but no psi. Main difference between the two pumps is the FI pump has a built in one way valve and working with the reg can generate the higher pressure.
If you think about it a stock /4 FI reg may be set to higher psi but it's still bypassing 99% of the time.




No difference, in theory C would be slightly better because it's always cool fuel right at the carb.
By that logic in a FI system each injector down the line would have less pressure, which is not the case.
In layman's terms think of it like a parallel vs series electrical circuit, parallel doesn't lose voltage. The fuel circuit flow is much like a parallel circuit, therefore no pressure drop.
Note that in C the fuel just bypasses through the carb inlet port, it doesn't go into the float bowl and back out.

The PMO fuel rails are made so you can screw small pre-filters in them.

Before you go too far, just remember there's scores of cars out there with low pressure rotary fuel pump (with a 3.5 psi output) feeding two carbs without a fuel pressure regulator, or return line, and running just fine.

I wouldn't use an Airtex even if I owned a parts store, they a junk

I have those PMO rails in a 'loop' configuration which years ago I speculated would help with distribution and cooling a bit and it has worked-out well. There is a small inline filter before the rails and a larger Canton canister-type filter closer to the pump up front. All the lines are AN-6 or hard metal.

Click to view attachment

Here is my bypass fuel system:
Supply line to shut off valve so that I can change out the fuel filter without mess.
Fuel filter.
Holley Blue pump
Holey Bypass regulator, 4.5 to 9 psi adjustable
Fuel cell in stock tank showing vent and return lines
Second Holley regulator in engine bay, 1-4 psi adjustable. 1 port in, 2 ports out.
Webers like 3.5 psi. Higher psi can push fuel past the float valves.
Individual lines to carb float bowls. I prefer the fuel rail setup that Chris C has but didn't go that way when I put this together 12 years ago. Also Chris' engine bay looks a whole lot cleaner than mine.
Needed the high volume Holley Blue pump to keep my thirsty 3.4l fed. Totally reliable in many years of track duty.


Click to view attachment Click to view attachmentClick to view attachmentClick to view attachment

Steve. Do you run the fuel pressure regulator all the time or just install it to test?

All the time. The low pressure regulator (1-4 psi) didn't come in bypass style so I run the two regs in series.

Wait a minute! You have way to many spark plug wires!! What the....

So do I
The real biatch is you can't see the dizzy, or fan, in the 914.

In researching bypass regulators, another question has popped up. Is the 8mm return line large enough to handle the return flow from a stock EFI pump while maintaining a low 3-4 psi to the carbs? Aeromotive suggests a 3/8" (9.5mm) return line for most stock EFI pumps to prevent restricting return flow to the point it builds pressure above the regulator setpoint. Sounds like the setup I'm contemplating has been used successfully before but thought I'd check.

I wouldn't worry about it unless you have 500+HP and are running a much larger pump.

The return is low pressure as soon as the leaves the regulator. The only high pressure is from the pump outlet to the regulator, so technically stock location two 4" pieces of FI hose, four FI clamps and the plastic (or SS) fuel line is the only thing high pressure in the circuit.
Low pressure to the carbs, all the rest of the system is no pressure just flow.

If you want to do an experiment get a FI pump hook it to 10' of gas hose and T in a pressure gauge. You won't see any pressure on the gauge, not unless you stick something like a MIG welder tip in the end of the hose.
I've only tried this with a low pressure pump (carter) but a .024 Mig welder tip is what was needed to build 3 PSI.

I posted this on my build thread but thought I'd share it here for those not following my build. I tore apart my fuel tank over the weekend and stumbled on another good reason to run a fuel return on our cars. The picture below shows the fuel reserve can with supply exiting and return entering in the bottom of the can. In operation, the return line is constantly refilling the reserve fuel can to keep it full as the main tank drains and allows the pump to efficiently drain all the fuel in the tank. Without a return line, the pump is likely to become fuel starved before the tank is actually empty. And yes, I was happy to see how clean my tank is inside. Probably because the last tank of gas was old fashioned leaded gasoline with not ETOH.