Fuel Injection vs. Webers, what's the difference in plumbing/hardware between the 2 Options

[Type 47]

OK, i get carbs only need one fuel line, but hey, there are 2 sticking out of the bottom of the tank.

I Did the Tangerine SS lines to eventually go back to FI, but going with the Webers to get the thing up and running.

Out of the tunnel and into engine bay, what's going on with the orphan fuel line? Block it off out of the tank or in the engine bay? Which one gets blocked off? The one with the tank screen filter or the other?

And What the Hell is this little white tube? Is it for the FI or does it have some function with the carbs? I don't think so but I keep seeing this tube in my disassembly pics.

[914werke]

White line = Vacuum line for the charcoal vapor/fume recovery system

[Robarabian]

The one with the filter is the supply line. Do not block it off. Even with carbs you can and should run the return line. Weber makes a fitting for the dual carb setup that is a "T" banjo. You plumb supply to one side of it and run the other side to the return line. That way the fuel is being cooled and you wont vapor lock.

I assume you know you cant use the stock fuel pump, you need 3-5 psi, not 60.

IF you're not running the return line, then yes, you can cap it at the tank, not the line end, which would be real dangerous.

[type53]

The one with the filter is the supply line. Do not block it off. Even with carbs you can and should run the return line. Weber makes a fitting for the dual carb setup that is a "T" banjo. You plumb supply to one side of it and run the other side to the return line. That way the fuel is being cooled and you wont vapor lock.

I assume you know you cant use the stock fuel pump, you need 3-5 psi, not 60.

IF you're not running the return line, then yes, you can cap it at the tank, not the line end, which would be real dangerous.

[930cabman]

I have ran a one line system for many years, some guys will utilize a return line, but why?

Also, I run the Webers on several of my cars on 2 - 3 psi. They have never been fuel starved and Webers are sensitive to over pressuring.

[brant]

I have ran a one line system for many years, some guys will utilize a return line, but why?

Cooler fuel
Less vapor lock !
More hp

That’s why

[930cabman]

I have ran a one line system for many years, some guys will utilize a return line, but why?

Cooler fuel
Less vapor lock !
More hp

That’s why

Have never experienced any of the above symptoms

[Superhawk996]

I have ran a one line system for many years, some guys will utilize a return line, but why?

Cooler fuel
Less vapor lock !
More hp

That’s why

Have never experienced any of the above symptoms

Drive harder! (IMG:style_emoticons/default/laugh.gif)

Way back in my learning years I had Webers, a Facet pump, no fuel pressure regulator, and had blocked off the return line. No issues. Then I started auto crossing and running the car hard. Gradually . . . I learned both how to drive and why fuel pressure regulators and return lines are a good thing. School of hard knocks (IMG:style_emoticons/default/headbang.gif)

[BK911]

The one with the filter is the supply line. Do not block it off. Even with carbs you can and should run the return line. Weber makes a fitting for the dual carb setup that is a "T" banjo. You plumb supply to one side of it and run the other side to the return line. That way the fuel is being cooled and you wont vapor lock.

I assume you know you cant use the stock fuel pump, you need 3-5 psi, not 60.

IF you're not running the return line, then yes, you can cap it at the tank, not the line end, which would be real dangerous.

Just for clarification...
The pump does not produce 60 psi unless the system is designed that way.
With a supply and return line, the pump will not make anywhere 60 unless there are restrictions somewhere in the line.
The PMO fuel regulator is perfect for converting from FI to carbs.
With a stock pump, adjust the return pressure drop until the pressure hits ~4 psi.

[Superhawk996]

The PMO fuel regulator is perfect for converting from FI to carbs.
With a stock pump, adjust the return pressure drop until the pressure hits ~4 psi.

Generally speaking, it is bad practice to use a high pressure fuel pump intended for fuel injection to feed carbs.

Makes no sense to use a pump capable of 30 psi to feed 3 psi to carbs.

Pumping fuel up to high pressure and then regulating it down just adds extra heat to the fuel. There is a reason Porsche used a different low pressure fuel pump for the /6 carb equipped cars.

Then there is an added failure mode with a high pressure FI fuel pump. If the pressure regulator fails, you'll have high pressure fuel at the carbs which will completely overwhelm the float and flood the carb fuel bowls. Far better to have a low pressure (~5 psi pump) that is regulated to 3 psi. Then if the regulator fails, car will still run (but poorly).

[BK911]

Generally speaking, it is bad practice to use a high pressure fuel pump intended for fuel injection to feed carbs.

Makes no sense to use a pump capable of 30 psi to feed 3 psi to carbs.

Pumping fuel up to high pressure and then regulating it down just adds extra heat to the fuel. There is a reason Porsche used a different low pressure fuel pump for the /6 carb equipped cars.

Then there is an added failure mode with a high pressure FI fuel pump. If the pressure regulator fails, you'll have high pressure fuel at the carbs which will completely overwhelm the float and flood the carb fuel bowls. Far better to have a low pressure (~5 psi pump) that is regulated to 3 psi. Then if the regulator fails, car will still run (but poorly).

Sorry, not trying to argue, but I think it is important for others to understand the system.

Paragraph 1 and 2, no comment.

Paragraph 3: The pump does not produce high pressure, it only produces what it needs based on the pressure drop of the system. If there is no pressure drop, as in the pump is open ended, there will be next to zero pressure in the system. As you adjust the regulator, it imposes a restriction on the return side that increases the fuel pressure. You add just enough pressure drop for your desired psi.

Paragraph 4: PMO regulator is a mechanical regulator with a bolt that adds pressure drop to the system. It will not fail.

So in the diagram below, crank down on the regulator until pressure is set where you want it at the carbs. If the regulator is wide open, there will be very little overall pressure in the system. As you start cranking the regulator closed, it will increase the system pressure BEFORE the regulator.
The old school pressure regulators are crap and add the restriction before the carbs. For that type of regulator I completely agree with all your statements above.

[Superhawk996]

@bk911

I agree with your assessment. I was largely thinking of the old school regulators that go before the carb. I wasn’t looking at or thinking of the flow diagram for the PMO regulator. Thanks for sharing that and keeping me honest!

Since the fuel pump is a positive displacement pump, there is still some nuance but as long as the fuel return loop is not adding significant flow restriction, the pump wouldn’t be adding much heat gain to the fuel. I see your point.

To use an extreme example, if the pump was large as to be delivering 100 gallon/min flow, and you were trying to force all that flow that through 1/4” tube, you would end up with a significant pressure rise in the discharge tube, significant heat gain of the fluid, and poor pumping efficiency. I.e - it would be like a water brake dyno. (IMG:style_emoticons/default/happy11.gif) I know this is extreme and isn’t what you are proposing but speaks to the general idea of not using a pump displacing more volume than needed to achieve the desired operating pressure.

[brant]

Vapor lock is real

The reason thousands of us relocate our pumps

[914werke]

@bk911 What specific PMO Fuel Pump are you referring to?

[BK911]

Regulator, not pump.
With this regulator and proper fuel system, almost any fuel pump can be used.

https://patrickmotorsports.com/products/fue...=15351737614451

[BK911]

Supply on left bottom, return on left top.
Top left bolt restricts fuel flow and adds pressure to system at carb take offs at 2 face ports.

[Superhawk996]

Back in the day . . . . I could buy a whole 914 for $125 not just a regulator. (IMG:style_emoticons/default/unsure.gif) Well . . . maybe $500. (IMG:style_emoticons/default/av-943.gif)

I do like the dual regulated outlets rather than having one carb daisy chained to the other with associated pressure drop.

[Type 47]

White line = Vacuum line for the charcoal vapor/fume recovery system

OK, one end goes on the vapor recovery tank on top of the fuel tank. where does the other end go in the engine bay?

[Type 47]

The one with the filter is the supply line. Do not block it off. Even with carbs you can and should run the return line. Weber makes a fitting for the dual carb setup that is a "T" banjo. You plumb supply to one side of it and run the other side to the return line. That way the fuel is being cooled and you wont vapor lock.

I assume you know you cant use the stock fuel pump, you need 3-5 psi, not 60.

IF you're not running the return line, then yes, you can cap it at the tank, not the line end, which would be real dangerous.

OK, makes sense to prevent vapor lock. Yes, your assumption is correct. I ordered a new fuel pump with the SS lines.

you mean capping it in the engine bay would be unsafe!! Like the PO did in my pic. Not only did he cap it in the engine bay it looks like he used whatever screw was laying around.

[campbellcj]

FWIW my car has no return line either and I've never had noticeable adverse effects, but it has a completely custom fuel system too. Pump is a Holley Red in the front, with a large cleanable Canton filter. All solid and AN-6 lines.