Bypass Regulator with Mechanical Fuel Pump?

EngineerDoug

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Hello,

I am presently running a Carter M6903 mechanical pump and a deadhead style regulator on a 550 inch six pack engine. This system is giving me some issues with idle characteristics once the engine heat soaks. I will be installing carb spacers but also looking to run a return line back to the tank. I intend to use a return style regulator after the carb feed so the fuel flows past the carburetors.

Here's my question - why does Holley (for example) state that their bypass style regulators cannot be used with a mechanical fuel pump? What will happen if I do?

I would rather not convert the system over to an electric pump, unless I have no other choice. Not keen on the added expense, noise, and added wiring/plumbing that go with an electric pump if I can avoid it.

Any advice is welcome - thanks.
 

Beekeeper

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Aeromotive has a nice bypass regulator that works with a mechanical pump. I will be using a bypass regulator on my hemi along with an edelbrock mechanical pump and I don’t see why a mechanical pump would make any difference to the regulator.
 

oldkimmer

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Why not get a fuel filter with the return line nipple on the side of it? Or would that not work with your regulator. Holley also says not to run diesel thru their electric pumps. Ive used them on my dodge diesels for 20 years. Kim
 

RemCharger

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One neat thing about mechanical pumps is their ability to turn nice cool fuel into 190 degree bubbling stew.

Fuel heaters you might say.
 

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Aeromotive has a nice bypass regulator that works with a mechanical pump. I will be using a bypass regulator on my hemi along with an edelbrock mechanical pump and I don’t see why a mechanical pump would make any difference to the regulator.
I have that setup in my '70 Charger. I don't recall the part numbers but I have a Carter mechanical pump that puts out 11 psi at idle. I installed the Aeromotive regulator with a return line to the tank. The fuel is constantly in a loop. This cleared up all of my vapor lock problems. I can drive in 110 degree heat and the car runs fine.
 

EngineerDoug

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I've seen the fuel filters with the built-in return. It's a good idea, but I am looking to run the fuel past the carburetor feeds before returning to tank. That should give me more cooling than bypassing before the carb feeds.

Note I am also experimenting with another idea - this might alleviate the need for a bypass regulator after the carb feeds. The idea is to use a small orofice/restrictor in the return circuit. Here are the elements, in order -

1) mechanical fuel pump
2) fuel pressure regulator - non bypass style
3) fuel filter
4) carburetor feeds
5) return line, with restrictor, back to tank

As long as the controlled "leak" back to the return circuit does not monkey with my pump or regulator, this might give me the circulation I am after. But if it doesn't, then I will have to use a bypass style regulator in place of the metering orofice. Hence my question about regulator suitability.

Thanks.
 

Dan64

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Carter says not to use a return line with their mech. pumps, messes with the internal bi-pass. I haven't done it yet myself but i would try the filter with the second outlet fot vapor. I would imagine thats all that is needed to stop vapor lock, the vapor is formed in the pump from heat and the vapor doesn't allow liquid gas to flow to carb so the best way would be to get rid of the vapor as soon as posible with the filter right after the pump. I beleive that you could get them with differnt size vapor ports, i think that Uncle Tony ( You tuber) did a video on this.
 

Dan64

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I've seen the fuel filters with the built-in return. It's a good idea, but I am looking to run the fuel past the carburetor feeds before returning to tank. That should give me more cooling than bypassing before the carb feeds.

Note I am also experimenting with another idea - this might alleviate the need for a bypass regulator after the carb feeds. The idea is to use a small orofice/restrictor in the return circuit. Here are the elements, in order -

1) mechanical fuel pump
2) fuel pressure regulator - non bypass style
3) fuel filter
4) carburetor feeds
5) return line, with restrictor, back to tank

As long as the controlled "leak" back to the return circuit does not monkey with my pump or regulator, this might give me the circulation I am after. But if it doesn't, then I will have to use a bypass style regulator in place of the metering orofice. Hence my question about regulator suitability.

Thanks.
I also tried this with a Enderel ( sold by Clay Smith) adjustable inline check value. Basically i had it installed after the carb , in-line in the return line . Both supply and return were -8an. The car ran ok but it wouldn't hold a steady pressure with the gauge bouncing from 51/2 -71/2 pounds very quickly. I wanted to try it out because to me it seemed more logical to regulate after the carb, giving the mechanical pump every chance to keep up but the the pump didn't like it
 

Dragon Slayer

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Mechanical fuel pumps are constant volume diaphragm pump, with variable volume based on motor rpm. Electric pumps are constant volume regardless of engine rpm. The mech also do not have the typical higher pressure an electric pump can attain. So the regulator sees a constantly changing input pressure, that electric has a more stable input pressure for the regulator and bypass.
 

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I finished plumbing in the Aeromotive 13301 bypass regulator; works fine. I was surprised to find the Carter mechanical pump puts out 10 psi unregulated.

With the bypass regulator installed I get a steady 6 psi.
 

Dean Prevolos

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I finished plumbing in the Aeromotive 13301 bypass regulator; works fine. I was surprised to find the Carter mechanical pump puts out 10 psi unregulated.

With the bypass regulator installed I get a steady 6 psi.

Can you post a photo of the bypass regulator installation?
 

old guys rule

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Hello,

I am presently running a Carter M6903 mechanical pump and a deadhead style regulator on a 550 inch six pack engine. This system is giving me some issues with idle characteristics once the engine heat soaks. I will be installing carb spacers but also looking to run a return line back to the tank. I intend to use a return style regulator after the carb feed so the fuel flows past the carburetors.

Here's my question - why does Holley (for example) state that their bypass style regulators cannot be used with a mechanical fuel pump? What will happen if I do?

I would rather not convert the system over to an electric pump, unless I have no other choice. Not keen on the added expense, noise, and added wiring/plumbing that go with an electric pump if I can avoid it.

Any advice is welcome - thanks.
Why not use a small cheap electric pump like edelbrocks with a switch to refill the carb on a hot soak?
 

EngineerDoug

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Here is a shot of the return regulator setup:

IMG_2044.JPG
 

EngineerDoug

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Just an update on this install - it works great. The fuel lines and fuel bowls are hardly warm to the touch after the engine fully warms up. The idle characteristics are a lot more stable as the engine reaches full heat soak. I added a Schrader valve at the regulator so I can check fuel pressure without a full time gauge, BTW.

Should have done it sooner.
 

old guys rule

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Just an update on this install - it works great. The fuel lines and fuel bowls are hardly warm to the touch after the engine fully warms up. The idle characteristics are a lot more stable as the engine reaches full heat soak. I added a Schrader valve at the regulator so I can check fuel pressure without a full time gauge, BTW.

Should have done it sooner.
Would you please do me a favor and post a drawing of the final setup that you have now. I can't make out how you have plumbed it from the picture. Thanks in advance, Dave
 

EngineerDoug

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I don't have a drawing but let me describe it for you:

1) Factory six pack fuel line setup uses a short length of hard line bent at 90 degrees to feed the last carburetor (rearmost). This line is fed from a brass tee (call it #2) that accepts inverted flare hardline.

2) Remove this line.

3) Run a short length of inverted flare hard line from the existing brass tee (#2) to a new brass tee. You can see this tee just above the coil tower.

4) This brass tee now has two outlets - one will feed the last carburetor via another short length of hard line. The other outlet (facing rearward) will feed the bypass regulator through a straight length of hard line.

5) Mount the regulator on a bracket and feed its inlet port via that hard line.

6) Lastly, plumb the regulator outlet port to your fuel tank return line. This outlet port faces downward, so you can't see it in the photo.

So you will need several items: a brass tee, three short hard lines, a bypass regulator, a bracket to mount it (I fabricated mine and used one of the end carburetor mounting bolts to secure it), and a fuel return line to the tank. And one or two brass adapters to go from inverted flare to NPT as needed. Plus a couple of NPT plugs to seal up any unused regulator ports. Note all of the hard line fittings are inverted flare, and there are some gentle bends in these lines to fit everything together. If you desire, you can also add a Schrader valve on one of the unused regulator inlet ports. You can see this fitting between the base of the coil and the MSD box.

I will also add an endorsement for the Eastwood flaring tool. All 3 of the hard lines were cut and shaped by hand, so I had to make my own double flares. I've used the cheapie flaring tools before and usually wind up throwing them across the garage. The Eastwood tool is a bit pricey but it yields a perfect flare with ease.

Your setup may be a bit different, especially if you are not running a six pack, but the gist of it is that the fuel flows from right to left, into the new tee, up to the last carburetor, rearward to the regulator, and then straight down to the return line.

Let me know if I can help further.
 

old guys rule

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I don't have a drawing but let me describe it for you:

1) Factory six pack fuel line setup uses a short length of hard line bent at 90 degrees to feed the last carburetor (rearmost). This line is fed from a brass tee (call it #2) that accepts inverted flare hardline.

2) Remove this line.

3) Run a short length of inverted flare hard line from the existing brass tee (#2) to a new brass tee. You can see this tee just above the coil tower.

4) This brass tee now has two outlets - one will feed the last carburetor via another short length of hard line. The other outlet (facing rearward) will feed the bypass regulator through a straight length of hard line.

5) Mount the regulator on a bracket and feed its inlet port via that hard line.

6) Lastly, plumb the regulator outlet port to your fuel tank return line. This outlet port faces downward, so you can't see it in the photo.

So you will need several items: a brass tee, three short hard lines, a bypass regulator, a bracket to mount it (I fabricated mine and used one of the end carburetor mounting bolts to secure it), and a fuel return line to the tank. And one or two brass adapters to go from inverted flare to NPT as needed. Plus a couple of NPT plugs to seal up any unused regulator ports. Note all of the hard line fittings are inverted flare, and there are some gentle bends in these lines to fit everything together. If you desire, you can also add a Schrader valve on one of the unused regulator inlet ports. You can see this fitting between the base of the coil and the MSD box.

I will also add an endorsement for the Eastwood flaring tool. All 3 of the hard lines were cut and shaped by hand, so I had to make my own double flares. I've used the cheapie flaring tools before and usually wind up throwing them across the garage. The Eastwood tool is a bit pricey but it yields a perfect flare with ease.

Your setup may be a bit different, especially if you are not running a six pack, but the gist of it is that the fuel flows from right to left, into the new tee, up to the last carburetor, rearward to the regulator, and then straight down to the return line.

Let me know if I can help further.
 

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