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> Dual Weber 40’s, Fuel lines
KevinW
post May 22 2020, 11:43 AM
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I am looking for a drawing or detail Or picture how to route the fuel lines. I have searched the web but no luck. I have an idea about the supply line but not sure about the return line?
Thanks
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brant
post May 22 2020, 01:29 PM
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this has been a controversial topic for ever...
a lot of people argue that you don't need a return line with carbs

technically the car will run without the return

however there is a reason that even the factory bothered to run a return line
it is the industry standard
it reduces fuel percolation, vapor lock
it also should theoretically produce more HP with cooler fuel

Here is a diagram that has been floating around this website for 15 years or longer:


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bbrock
post May 22 2020, 01:48 PM
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There is another reason to keep the return line. The reserve fuel system depends on it. In the pic below, you can see that the supply line drains from a bowl in the bottom of the tank and the return dumps fuel back in it. This allows the system to constantly scavenge fuel from the tank and concentrate it in that bowl so you can use all of the fuel before sucking air. I've read of people complaining that their car was running out of gas with the gauge showing 1/8 or more of a tank after switching to carbs. I'm guess this is why.

(IMG:http://www.914world.com/bbs2/uploads/post-20845-1587959064_thumb.jpg)
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Superhawk996
post May 22 2020, 02:05 PM
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QUOTE(bbrock @ May 22 2020, 03:48 PM) *

There is another reason to keep the return line. The reserve fuel system depends on it. In the pic below, you can see that the supply line drains from a bowl in the bottom of the tank and the return dumps fuel back in it. This allows the system to constantly scavenge fuel from the tank and concentrate it in that bowl so you can use all of the fuel before sucking air. I've read of people complaining that their car was running out of gas with the gauge showing 1/8 or more of a tank after switching to carbs. I'm guess this is why.

(IMG:http://www.914world.com/bbs2/uploads/post-20845-1587959064_thumb.jpg)


Good point but not entirely correct. You can run them dry without a return line. Ask me how I know. (IMG:style_emoticons/default/laugh.gif)

Fuel will still enter the "coffee can" as low fuel sloshes to and fro. You'll notice the holes in/out of the coffe can are quite small. So they effectively act as an orifice to restrict flow out of the can concentrating fuel around the pickup inlet. Also the inlet is situated at the low point and all other sufaces slope toward the coffee can to try to feed it.

In my case I did get episodes of running then stalling that came a mile or so in advance of when I had to walk to the gas station so I'll readily concede that a return line may have helped prvent that. But at the end of the trip, when the gas is gone, your walking. (IMG:style_emoticons/default/sad.gif)

I'm wondering if those with the 1/8 tank scenario were running around with debris plugging the coffee can in/out orifice holes.

Fully concur that return line is the modern, proper solution that will help cool fuel and reduce vapor lock. I did what I did (not using return) before I knew any better.
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SKL1
post May 22 2020, 02:06 PM
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That makes sense but I've been running carbs on both 914's for more than 30-40 years and never had an issue without a return line. I did move the fuel pump up front on both though.
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bbrock
post May 22 2020, 03:27 PM
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QUOTE(Superhawk996 @ May 22 2020, 02:05 PM) *

I'm wondering if those with the 1/8 tank scenario were running around with debris plugging the coffee can in/out orifice holes.


I just assumed the engine was being starved when they cornered. Obviously if the car is running level you would be able to run them dry because I don't think the supply/return tubes make a liquid tight seal with the can, but that isn't how we are supposed to drive these cars. (IMG:style_emoticons/default/biggrin.gif) I would prefer to have my last quart of fuel in that bowl rather than sloshed up against the far end of the tank. Also, with the orifice holes half way up the sides of the can, I'm not sure how much fuel would wind up sloshing into the can when the tank gets low.

I also ran a 914 and a bus on carbs without return lines. I really can't remember if there were any issues with stuttering as the tanks got low. Didn't do a lot of hard cornering in the bus though as I had an annoying habit of not wanting to tip it over. (IMG:style_emoticons/default/laugh.gif)
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Superhawk996
post May 22 2020, 03:48 PM
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QUOTE(bbrock @ May 22 2020, 05:27 PM) *

QUOTE(Superhawk996 @ May 22 2020, 02:05 PM) *

I'm wondering if those with the 1/8 tank scenario were running around with debris plugging the coffee can in/out orifice holes.


I just assumed the engine was being starved when they cornered. Obviously if the car is running level you would be able to run them dry because I don't think the supply/return tubes make a liquid tight seal with the can, but that isn't how we are supposed to drive these cars. (IMG:style_emoticons/default/biggrin.gif) I would prefer to have my last quart of fuel in that bowl rather than sloshed up against the far end of the tank. Also, with the orifice holes half way up the sides of the can, I'm not sure how much fuel would wind up sloshing into the can when the tank gets low.

I also ran a 914 and a bus on carbs without return lines. I really can't remember if there were any issues with stuttering as the tanks got low. Didn't do a lot of hard cornering in the bus though as I had an annoying habit of not wanting to tip it over. (IMG:style_emoticons/default/laugh.gif)


I'll have to look at my tank closer again to see where my coffee can orifice holes are, I think there are two or four much smaller holes down by the bottom of the coffee can.

I don't recall having any gas left at all when I looked in the tank but I also didn't have a good bright flashlight looking in there. That was the era of dim bulb 2AA cell Mag light in glovebox and I was looking though the filler hole itself so can't see as much as you've shown in the photo when you can pull the whole filler assembly.

Granted I wasn't cornering like an AX or track situation when I ran out but I was on curvy roads (North Michigan remember, not CA canyon roads). I got some sputtering in the corners (long below 1/8 tank), slowed down when I looked at the guage and realized how screwed I was. I then tried to limp it at 40-45 mph into town. Almost made it. (IMG:style_emoticons/default/av-943.gif)

Now I'm super curious!
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bbrock
post May 22 2020, 04:06 PM
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QUOTE(Superhawk996 @ May 22 2020, 03:48 PM) *

Now I'm super curious!


The contraption looks very ingenious to me (clever Germans). It looks like the can is designed to be leaky so it can fill from the tank but drain a little slower than it gets refilled by the return pump. The result being that as the tank gets low, there is a little can full of fuel not sloshing around too much to keep the supply tube submerged. Seems pretty nifty.
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ChrisFoley
post May 22 2020, 05:20 PM
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I have never used a return line on a carbed car and I have never had a problem from following that design.
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IronHillRestorations
post May 22 2020, 06:14 PM
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I'm with Chris on this. I've never run a return line on a carbureted engine. That's not to say that Brant isn't right, in that a return line system with a bypass regulator is probably theoretically the optimum.

There's two basic types of regulators; blocking and bypass. Where and how you use them is the important part. You can also get a bypass regulator that can be controlled with vacuum so you get the optimum pressure at all times.

For a street 914 I've had great results with the correct fuel pump direct to the carbs. KISS
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KevinW
post May 22 2020, 06:34 PM
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I will be using a Facet fuel pump. When not using a return line do you cap the return at the fuel tank?
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bbrock
post May 22 2020, 06:47 PM
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QUOTE(IronHillRestorations @ May 22 2020, 06:14 PM) *

You can also get a bypass regulator that can be controlled with vacuum so you get the optimum pressure at all times.


Can you explain a little more about this type? I'm shopping for a bypass regulator now and had pretty much settled on the PMO, but interested about the theory behind a vacuum controlled regulator and where to find them. I hadn't come across them and it's a part of the car I'd like to know more about.

QUOTE(KevinW @ May 22 2020, 06:34 PM) *

I will be using a Facet fuel pump. When not using a return line do you cap the return at the fuel tank?

Facet pumps will drive you batty with the noise. I've used them. They work, but are about as fun as having a hairy nun drum her fingers on your skull for hours on end. Never again.
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SirAndy
post May 22 2020, 08:09 PM
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QUOTE(bbrock @ May 22 2020, 05:47 PM) *
Facet pumps will drive you batty with the noise. I've used them. They work, but are about as fun as having a hairy nun drum her fingers on your skull for hours on end. Never again.

(IMG:style_emoticons/default/agree.gif) Rotary pumps are the way to go ...
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mtndawg
post May 22 2020, 10:25 PM
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QUOTE(SirAndy @ May 22 2020, 06:09 PM) *

QUOTE(bbrock @ May 22 2020, 05:47 PM) *
Facet pumps will drive you batty with the noise. I've used them. They work, but are about as fun as having a hairy nun drum her fingers on your skull for hours on end. Never again.

(IMG:style_emoticons/default/agree.gif) Rotary pumps are the way to go ...

Yes I have a rotary pump and no return line and it runs great!


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ndfrigi
post May 23 2020, 01:23 AM
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QUOTE(mtndawg @ May 22 2020, 09:25 PM) *

QUOTE(SirAndy @ May 22 2020, 06:09 PM) *

QUOTE(bbrock @ May 22 2020, 05:47 PM) *
Facet pumps will drive you batty with the noise. I've used them. They work, but are about as fun as having a hairy nun drum her fingers on your skull for hours on end. Never again.

(IMG:style_emoticons/default/agree.gif) Rotary pumps are the way to go ...

Yes I have a rotary pump and no return line and it runs great!



sorry Kevin to change topic! @mtndawg do u mind sharing what kind of catch can or breather do u have attached to rear wall and where is that white line goin?

thank you!

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ChrisFoley
post May 23 2020, 09:58 AM
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QUOTE(KevinW @ May 22 2020, 08:34 PM) *

I will be using a Facet fuel pump. When not using a return line do you cap the return at the fuel tank?

The answer is yes. A short piece of fuel hose, a 5/16" long (2+ inches) bolt with all the threads cut off and two hose clamps is all you need.
Facet interruptor pumps (the square ones) are generally reliable and have been used by 914 owners successfully many times in the past. Usually a pressure regulator is required since they put out 6-8 psi which is too much for the carburetor needle valves.
OTOH, most of the available rotary pumps are internally regulated to 3 1/2 psi and no external regulator is required.
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Ansbacher
post May 23 2020, 11:24 AM
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The inventor of the Facet type pump is now sitting in a locked room in hell with 500 Facet pumps running simultaneously. Go rotary!

As far as return lines- never used one and have never had any issues.

Ansbacher
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IronHillRestorations
post May 23 2020, 12:13 PM
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I may have been talking through my hat. There used to be a few different vacuum compensated fuel pressure regulators, but I did a search and didn't come up with much, except some very high dollar race car parts.

Like many others have posted, get a good quality 3.5 psi rotary fuel pump and you'll be good to go. If you have to use a solid state ratta-ratta-ratta pump, you can minimize the noise with rubber mounts
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mtndawg
post May 23 2020, 01:19 PM
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QUOTE(ndfrigi @ May 22 2020, 11:23 PM) *

QUOTE(mtndawg @ May 22 2020, 09:25 PM) *

QUOTE(SirAndy @ May 22 2020, 06:09 PM) *

QUOTE(bbrock @ May 22 2020, 05:47 PM) *
Facet pumps will drive you batty with the noise. I've used them. They work, but are about as fun as having a hairy nun drum her fingers on your skull for hours on end. Never again.

(IMG:style_emoticons/default/agree.gif) Rotary pumps are the way to go ...

Yes I have a rotary pump and no return line and it runs great!



sorry Kevin to change topic! @mtndawg do u mind sharing what kind of catch can or breather do u have attached to rear wall and where is that white line goin?

thank you!

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I think I found this on eBay or amazon. It’s aluminum, size is nice and black to match the tin. Venting out the rain tray tubing hole on the driver side. I’ve thought about going back into the engine through the air intake and making a manifold for the intake to clean things up a bit. It’s on my to do list.


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ndfrigi
post May 23 2020, 02:10 PM
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QUOTE(mtndawg @ May 23 2020, 12:19 PM) *

QUOTE(ndfrigi @ May 22 2020, 11:23 PM) *

QUOTE(mtndawg @ May 22 2020, 09:25 PM) *

QUOTE(SirAndy @ May 22 2020, 06:09 PM) *

QUOTE(bbrock @ May 22 2020, 05:47 PM) *
Facet pumps will drive you batty with the noise. I've used them. They work, but are about as fun as having a hairy nun drum her fingers on your skull for hours on end. Never again.

(IMG:style_emoticons/default/agree.gif) Rotary pumps are the way to go ...

Yes I have a rotary pump and no return line and it runs great!



sorry Kevin to change topic! @mtndawg do u mind sharing what kind of catch can or breather do u have attached to rear wall and where is that white line goin?

thank you!

Attached Image


I think I found this on eBay or amazon. It’s aluminum, size is nice and black to match the tin. Venting out the rain tray tubing hole on the driver side. I’ve thought about going back into the engine through the air intake and making a manifold for the intake to clean things up a bit. It’s on my to do list.


so the line is just going down the floor.
thank you for sharing. Oh that is a clean engine bay!

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