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Old 10-31-2009, 12:48 AM
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Default Fuel Pressure Regulator location

Hi all, I have a question for those of you running Webers. Where did you mount your fuel pressure regulator in relationship to your carbs and fuel pump. I am installing a stroked 351 in a 65 Mustang and have purchased a bypass regulator that I plan on running a return line back to my tank with. My question is do I mount it directly before the first carb, after the last carb, or is it ok to mount the regulator to an inner fender about three feet before the first carb. Any advice is welcome. One more thing, I am using an electric fuel pump mounted near the tank. Thanks for the time.
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Old 10-31-2009, 03:09 AM
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Paul,

I run a Mallory 3 port bypass regulator.

My system is plumbed splitting the main supply line to the rear carbs, then to the front carbs, then off the front carbs to either side of the reg, then out the bypass and back to the tank on the return line.
My pressure gauge is mounted on the side of the regulator.

My reg is mounted after the carbs as above, with a bypass reg this is the best way, that way the carbs are getting fresh unheated fuel.
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Old 10-31-2009, 06:49 AM
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I agree with Gary. The regulator must go after the carbs. The gauge can go anywhere before the regulator or just mount it on the regulator.
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Old 10-31-2009, 07:13 AM
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Old 10-31-2009, 11:40 PM
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Thank you all for the replies. One more question if I may, what size lines are you running for the feed and return. I was originally going to run a 3/8" feed line and a 5/16" return line, but in reading the instructions on the regulator it recommends the same size line or larger for a return. What is working for you guys? Thanks Again.
Paul
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Old 11-01-2009, 03:17 AM
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Paul, I run 3/8 on both, the bypass sends excess back to the tank,
so at ignition on engine off ALL the fuel is going in a loop back to the tank.

If the return is restrictive compared to the supply line, the fuel pressure may be higher than with the engine running and flooding will result.

Of course it also depends on whether you want your pump running at IGN on to prime the carbs prior to fire up.
You can still have a pump disable (via oil pressure switch etc) at stall condition, ie accident (heaven forbid).
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Old 11-01-2009, 11:11 PM
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Thanks to all who answered, I think that I know what I will do.
Sincerely,
Paul
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Old 11-02-2009, 07:53 AM
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Am I missing something here? I thought the regulator had to be mounted between the fuel pump and the carbs, and as close to the carbs as possible. The guage can be mounted after the carbs. If you mount the regulator after the carbs, then how can you adjust the fuel pressure?

The fuel pressure regulator is there to regulate the fuel pressure to the carbs, just under 3 lbs for Webers. You need a return line so the excess pressure can be bypassed.
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Old 11-02-2009, 01:32 PM
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Quote:
Originally Posted by Snakebit View Post
Am I missing something here? I thought the regulator had to be mounted between the fuel pump and the carbs, and as close to the carbs as possible. The guage can be mounted after the carbs. If you mount the regulator after the carbs, then how can you adjust the fuel pressure?

The fuel pressure regulator is there to regulate the fuel pressure to the carbs, just under 3 lbs for Webers. You need a return line so the excess pressure can be bypassed.
A bypass regulator can be mounted before OR AFTER the carbs.

The regulator is not a restriction for fuel flow if after the carbs.

Mounted after, the carbs are getting fresh cool fuel at their inlets,
the regulator dumps the excess back to the tank just like EFI does but at a lower pressure. Mine runs at 3 psi.
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Old 11-02-2009, 02:33 PM
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So if my mechanical pump is putting out 7psi, and I place a regulator, with a bypass set at 3 psi, at the end of my Weber set up, all the carbs will be getting fuel at 3psi??? I would think the first carb would be getting fuel at 7psi???
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Old 11-02-2009, 03:07 PM
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Quote:
Originally Posted by Snakebit View Post
So if my mechanical pump is putting out 7psi, and I place a regulator, with a bypass set at 3 psi, at the end of my Weber set up, all the carbs will be getting fuel at 3psi??? I would think the first carb would be getting fuel at 7psi???
No, the regulator will send the excess back to the tank.
The pressure between the pump and the reg as seen by all the carbs SHOULD be what pressure the reg is set at. You could fit the gauge at each carb in turn to prove this.

I wouldn't do a bypass reg setup with a mechanical pump since the pump will always be "pumping" unlike when the mechanical pump "idles" when fuel pressure is up.
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Old 11-03-2009, 08:22 AM
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I guess I could see with an electrical fuel pump and a bipass regulator it does not matter where you mount it, but for a mechnical fuel pump and a non bypass regulator, the regulator would have to be in front of the carbs to work properly. Wouldn't it? I have a non bypass regulator (mechanical fuel pump) BEFORE my webers and it seems to work fine.
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Old 11-03-2009, 10:14 AM
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To some extent IMO this whole thing about where to put the regulator is over done. Its all about hydraulics. The pressure is going to be the same throughout the line whether it is place before OR after the carbs. The reason for having the regulator in the first place is to limit the line pressure because the design of the Needle/seat and the mechanical leverage imposed by the Weber design float is not capable of creating a leak free seal when the pressure is much above 3 lbs. There is no "Cushion" at the point of seal as in a Holley because the Needle/Seal assembly is made completely of Brass without any Viton tip (which would be a great improvement), or if the Groose brand (sp?) ball type valve were still available in any size but 3.0.
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Old 11-03-2009, 02:05 PM
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I have to agree with Rick. I think more importantly the question should be asked, Do I run a return or a dead head regulator.

Majority of the books recommend a dead head reg. however, I am running a return (bypass). There are very few reg. that will operate at 3 psi that are designed for a bypass setup.

I have heard that there is a improvement in perform (night / day difference) with using a dead head regulator. When I was using a dead head by carbs were not properly tuned, so I am have not tested it, maybe that person will chime in to share his results.

I do remember my pressure would creep higher than 3 psi until heat set in than the pressure would lower.

There is a thread on this on CC with this concern. If I remember correctly, this is why I went to a bypass style, along with having cooler fuel circulation.
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Old 11-03-2009, 06:41 PM
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I use a non adjustable bypass regulator from Kinsler for my Webers with a return line. It was preset to 3 psi, nothing to adjust. I do disagree(if I understand the conversation correctly) with the flexibility of the mounting location. A bypass regulator must go after the carbs with a return line to regulate the pressure before the regulator and a regular regulator must go before the carbs with a dead head setup to regulate the pressure after the regulator.
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Old 11-03-2009, 10:21 PM
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Quote:
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I use a non adjustable bypass regulator from Kinsler for my Webers with a return line. It was preset to 3 psi, nothing to adjust. I do disagree(if I understand the conversation correctly) with the flexibility of the mounting location. A bypass regulator must go after the carbs with a return line to regulate the pressure before the regulator and a regular regulator must go before the carbs with a dead head setup to regulate the pressure after the regulator.
Fully agree.
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Old 11-04-2009, 12:22 PM
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I have a Mallory bypass regulator mounted before the Webers (see pics in gallery) using an Edelbrock machanical 7psi street pump. The regulator is set at 2 3/4 lbs. If the pressure exceeds the preset amount the diaphram opens and allows the excess pressure to bypass back to the tank. Is this correct, or is the last carb getting less fuel presure than the first?
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Old 11-04-2009, 03:36 PM
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Quote:
Originally Posted by Snakebit View Post
I have a Mallory bypass regulator mounted before the Webers (see pics in gallery) using an Edelbrock machanical 7psi street pump. The regulator is set at 2 3/4 lbs. If the pressure exceeds the preset amount the diaphram opens and allows the excess pressure to bypass back to the tank. Is this correct, or is the last carb getting less fuel presure than the first?
Technically the fuel between the reg and all the carbs "should be" at the same pressure within the "rail" similar to EFI.
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Old 11-06-2009, 04:23 AM
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Default Same here.

Quote:
Originally Posted by Snakebit View Post
I have a Mallory bypass regulator mounted before the Webers (see pics in gallery) using an Edelbrock machanical 7psi street pump. The regulator is set at 2 3/4 lbs. If the pressure exceeds the preset amount the diaphram opens and allows the excess pressure to bypass back to the tank. Is this correct, or is the last carb getting less fuel presure than the first?
Hi.
I use the same set- up. 3/8" tube (AN6) from Summit fuelpump.
Goes into Aeromotive fuel regulator (comes w/ 2 springs: 1 for carb, 1 for injection. Also for turbo- /supercharging).
From there splits into two, one line (AN6) to each row of carbs.
Return line is 1/2" (AN8).

PS: A friend of mine tried smaller return line and got into trouble. Fuelregulator didn't bring pressure down to 3 PSI, not lower than 4. Resulted fuel overflow.. Changed to 1/2" and it was all smooth.
He did have a pump with rather high flowrate end pressure, so it all depens on. Anyway the return line has to have capacity enough to drain out the excess fuel.

Never found any issues with front carbs. Should work as GAZ zez... Unless the pump cannot hold up for the fuel demand.... Then the front carbs will get into trouble, as far as I can tell.

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Old 06-14-2016, 07:00 PM
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What regulator does anyone recommend for a 427 fe. I heard the Mallory 4309 is often used. Anyone use it.
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