Fuel pressure regulator plumbing : 850 Demon with a Carter mech. pump

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Kern Dog

Kern Dog

Build your car to handle.
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I recently removed my Holley mechanical fuel pump from the 493 because I suspected it might be contributing to a fuel delivery issue. It showed 6-7 lbs of pressure at idle. I bolted in a Carter and now the pressure is at 10-11. I suspect that prolonged driving would overwhelm the needle valves and flood the carb. I obviously need a regulator to make this pump work.
Several types are out there with a wide range of prices.
I first considered a return type. This would allow me to send fuel back to the tank through the stock replacement 1/4" vent line. I saw a schematic of a Mallory pump 7 regulator that showed the regulator mounted behind the "fuel log".( Behind the secondary fuel bowl) I'd figured to run the return line to the firewall then down to the RH frame rail. I was all ready to order the regulator and some fittings when the rep at Summit racing said that this location of the regulator wouldn't work. I don't know enough about it to put up a sensible arguement but I've seen the regulator in that position before.
I considered an "inline" type with no return line. This would simplify things but I'd lose the benefit of the cooling of the fuel by way of keeping the fuel in "a loop".
If I can't make any sense of this, I'll have to put the Holley pump back on. I'm leaving Thursday morning for the Spring Fling in Van Nuys.
Thanks, Greg
 
I don't exactly understand what you are proposing, but if you are referring to a 70 / later 1/4" factory line, you cannot simply hook up and use that line BECAUSE that is your vent line, and that will negate your vent.
 
There are regulations by sanctioning bodies that do not allow fuel lines or distribution stuff within so many inches of the flywheel or bellhousing area. It's a safety deal should something there let go and come out.
I've found it best to mount the regulator on the fenderwell and run lines to the carb/engine. The vibration is much less and the regulators seem to hold the pressure setting better and forever. The return should run parallel to the std fuel feed along the frame/floor, and to keep the pressure readings accurate, should be the same size or larger than the feed side.
 
Follow both above...need a dedicated return if you decide to install a regulator...repurposing the vent line for a return line can lead to overpressure problems if there's no other venting capability.
 
Use the vent for the return and simply run a vented gas cap. Problem solved.
 
I appreciate the responses.
The car is actually a 70 Charger. The replacement vent line has been capped since 2003 when I installed it. There are many 70 and 71 model Mopars like mine that have that strange vent tube in the trunk with 4 or 5 lines running to it. Mine is there and still functional. I have the stock type gas cap.
I am just going back and forth with whether or not to keep the Carter pump in there. The Holley ran decent pressure and required no regulator. I just thought it might be a contributor to the fuel starvation. Fact is, the car only bogged twice on me after several full throttle runs. The pushrod was the right length though so I thought maybe I needed the carter pump.
The reason I posted here is because the member traffic here seems to be twice what I see on FBBO. Thanks for any advice you are willing to give.
 
You should get a diagnostic fuel pressure gage and secure to the windsheild. Make a few full power runs and see what the presure's doing. I know enough about Demons that I frankly avoid them - they are very sensitive to atmospheric and fuel pressure. Overly so IMO. If the car does not slow down every time - I don't feel it's worth revamping the fuel system until you have proof there's an issue.
 
Last year during my quest to stop the detonation, I rigged a fuel pressure guage to a long rubber fuel line then taped the guage to the windshield so I could see the pressure at WOT. At idle it was 6-7 lbs and it never dropped below 5 at WOT.

I'm surprised that I was running 11 lbs and the car ran fine. I had 2 different guages on it with the same #s so I'm pretty sure the readings were accurate.

Today I pulled the Carter and put the Holley back on. The pressure was back between 6 & 7 lbs again and the car ran fine. I'll keep the Carter pump and maybe plumb a regulator and return line sometime later.
Thanks for the help guys, Greg
 
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