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Posted by: Type 47 Dec 8 2022, 03:53 PM

pictured is the carb setup from when I took the engine out.

It was a single line feed but I want to put a return line back to the tank.

Where would I T that in the plumbing?

Posted by: GregAmy Dec 8 2022, 04:57 PM

You will need to change to a return-type fuel pressure regulator, otherwise pressure would be almost zero as it flowed right back into the tank (easiest path).

The return will be on the bypass side of the pressure regulator.

Edit: something like this should work, mounted before the feed lines to the carbs: https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/regulators/carbureted_regulators/parts/12-887

Kinda curious: why? Worried about vapor lock? You're still going to have that last bit of feed to the carbs that will not be full flow, and that's the most-common locations for vapor lock.

Posted by: VaccaRabite Dec 8 2022, 06:09 PM

You need a regulator plumbed in. Metered output goes to the carbs, everything else is shunted back to the tank. Easy peasy. Just like stock but with a lot less pressure.

Zach

Posted by: Type 47 Dec 8 2022, 07:52 PM

So in the below thread (3rd post down), it was suggested to have a return line to avoid vapor lock. After reading the post again, I think I overlooked the answer the Weber banjo. but now I should investigate using a regulator also.

http://www.914world.com/bbs2/index.php?showtopic=362785

Posted by: VaccaRabite Dec 8 2022, 08:54 PM

Vapor lock tend to be more about where your pump is (early location low in the engine bay or late location in the front trunk). The early location would get hot, adding more heat to the fuel, making it more prone to lock. Also adding phenolic spacers to your intake runners does a LOT to fight vapor lock with carbs. Without the spacers, heat from the heads goes up the runners into the carbs and can boil the fuel in the bowls. A return line allows fuel to flow back into the tank instead of the fuel getting backed up behind the regulator/carbs and soaking up heat.

As to the regulator - there are only 2 ways to successfully run fuel to carbs. Using an internally regulated fuel pump, or using a fuel regulator. The regulated pumps are non-adjustable and you buy the one that has the right pressure (under 5 PSI). Regulators come in bypass or non-bypass versions. The stock regulator has a bypass, and the excess fuel goes back to the tank. Many carb regulators don't have a bypass, and are designed with only one line to be used (no return). This does require a low pressure fuel pump too - you can't use the stock pump regulated or not.

For whats its worth, I never ran a return line when my car had carbs, and I never had vapor lock issues. But my pump is in the front, and I was using phenolic spacers to block the head heat.

Zach

Posted by: brant Dec 9 2022, 08:38 AM

Zach

The factory ran a return line
All factories run a return line

Yes systems “can” work without
Especially at low altitude and in cool humid locations

But why direct folks to cut corners instead of doing things correctly

Posted by: brant Dec 9 2022, 08:39 AM

Plumbing options


Attached image(s)

Posted by: 914werke Dec 9 2022, 11:30 AM

Option E
Oh & "while your in there" you might consider tossing that X-bar linkage in the Bin & going with something better.

Posted by: JmuRiz Dec 9 2022, 01:06 PM

What do the symbols stand for.

Posted by: 914werke Dec 9 2022, 01:28 PM

Tank Carbs Pump Regulator Tee Lines

Posted by: brant Dec 9 2022, 01:45 PM

Plus fuel filter before the pump

Posted by: GregAmy Dec 9 2022, 01:59 PM

Oh the rectangle is the filter? I thought it was the pump. Makes a lot more sense now.

Rectangle = filter
Circle = pump (stock is internal bypass)
Hexagon = pressure regulator (some bypass, some not)
Ovals w/circles = 6-banger carbs.

Only option B or E with full-flow banjos will give you the vaporlock-proofing you want. I personally don't see it as necessary but it certainly will be better. - GA

Posted by: NARP74 Dec 9 2022, 02:19 PM

What does having the regulator after the carbs do for the system?

Posted by: Craigers17 Dec 9 2022, 02:33 PM

One option as posted from OP's other thread on related topic.

https://patrickmotorsports.com/products/fuepmofpran?variant=15351737614451

Posted by: GregAmy Dec 9 2022, 02:40 PM

Maintains desired pressure at the carbs and allows full fuel recirculation as close to the carb inlet as possible.

This is how the stock D- and L-Jet do it (as well as most legacy EFI systems) but at a higher pressure of course.

OEMs are moving to returnless systems for reduced hydrocarbon emissions and reduced complexity (my '08 Civic Si race car is returnless.) - GA

Posted by: Root_Werks Dec 9 2022, 04:07 PM

I've used that option picture before and really like "E". Circulating fuel back to the tank and grabbing cooler fuel to feed the carbs helps make for a stable system.

Posted by: nditiz1 Dec 11 2022, 07:17 AM

Here is how I mounted my PMO regulator. Originally when I had Zentihs I wasn't running one and even before that with dual dellortos I wasn't running one. I already have the cb performance rotary FP up front so this is a little overkill, but it allowed for a return and it came in my PMO kit so might as well.

Posted by: bbrock Dec 11 2022, 01:27 PM

I also like the "E" option but have been running "C" for 7K miles and it works well. Here's the regulator I'm running and it has worked well. The pressure to the carbs hasn't budged since originally setting to 3.5 psi.

https://www.ebay.com/itm/371739673458