Fuel Pressure issue and (at least partial) Solution

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73Dart340Sport

73Dart340Sport

73dart340
FABO Gold Member
Joined
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Good morning,

I have a few questions for the expert builders at FABO. Two years ago I had a reputable Mopar builder in the area re-build the top end of my 340 Dart Sport. He remedied the “sins” I committed in the 90’s when I attempted a Car Craft recipe build. Part of the build was 3/8” fuel line and a Carter performance fuel pump. After the rebuild, right sizing of the Cam and valve train, I’m left with a 9225S Thermoquad and the Carter pump. After trouble shooting and realizing that I was getting almost 11PSI at the carburetor I set about figuring out how to install a Holley 12-803 Dead-end regulator. This easily dropped the PSI to 5.5 and created vapor lock. Using the old 5/16” return line and a WIX 33040 filter the vapor lock problem went away.

My issue is that I’d like to relocate the pressure regulator closer to the carb and get rid of a lot of the rubber, and at the same time get the improved performance and ease of hot starting.

Would anyone have pictures and ideas as to the ultimate location for the regulator? Also, although I’m not married to the idea of keeping the mechanical pump, I’m also trying to stay away from completely reinventing the wheel over and over!

Thanks

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Just an idea but a long time ago I mounted that same reg to my throttle return spring bracket.
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That looks great. I’m not sure if I have the fabrication skills. That looks like a LA engine. How did you mount it on the manifold?
 

73Dart340Sport said:
That looks great. I’m not sure if I have the fabrication skills. That looks like a LA engine. How did you mount it on the manifold?
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It was a big block Chevy. But the bracket is just a cheapy from summit or something for throttle return springs and throttle cable. All I did was drill one big hole, and two small holes and dropped the reg right in.
IMG_1772.png

Started as something like this.
 
I was trying to match the hole in the rear with the distributor and the one in front. I was thinking it was one odd manifold. That makes sense. Just wasn’t expecting it in a Mopar forum.
 
73Dart340Sport said:
I was trying to match the hole in the rear with the distributor and the one in front. I was thinking it was one odd manifold. That makes sense. Just wasn’t expecting it in a Mopar forum.
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Lol. Yea I’ve got a bunch of different makes of stuff. That one was the first rebuild on the engine in my boat. It’s much different now.
 
Get rid of the reg & try another pump.....
That will get rid of a lot of rubber....& connections that can leak.
 
If yur talking the the P4007040 pump, I've been running that since around year 2000.
That thing is rated 80gph at 8.7psi. enough for any SBM.
My Holley 750 DP with stock inlet-valves has never had an issue with it. Actually, I have run several different carbs, including at least one TQ, and none have had an issue.
Sorry, I don't run a gauge so, I can't tell you what mine's running at.
I'm no fan of regulators and/or return lines.
So, if I needed less pressure, I'd be taking the pump apart for custom calibration.
 
Can you make your own hard line?
Use the regulator as a "T", hard line to each bowl. One pressure line into the bottom of the regulator. (Use a 90° fitting).
Could also use braided line. I'd recommend teflon. But I'd guess the fittings and line would approach $100
(I'm using a fuel log that came in my carb kit. Speedway asked over $100 for it separately. I would NOT spend that for it!)
 
33IMP said:
Can you make your own hard line?
Use the regulator as a "T", hard line to each bowl. One pressure line into the bottom of the regulator. (Use a 90° fitting).
Could also use braided line. I'd recommend teflon. But I'd guess the fittings and line would approach $100
(I'm using a fuel log that came in my carb kit. Speedway asked over $100 for it separately. I would NOT spend that for it!)
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I have made nycop lines. I have yet to do steel, but I’m considering it.
 
I use the same Holley dead head reg also, but I dont run a return line, that reg isnt made for one. Holley does make the same reg with a provision for a return line, it would make a much cleaner install if you go that route and keep the return line.
This is how I do mine, 6AN from mechanical pump to reg on inner fender, 6AN routed under the alternator and up to the fuel filter, gauge, then to carb.
Yes, I know I need to neaten the wires by the valve cover :lol:

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If all you want to do is run less rubber, another option is to run hard line on the chassis down to the frame rail then use short hoses at the rail for engine movement. Use common brake inverted flare to npt fittings on the regulator. Fit prefab ags steel or fab nicopp lines to run down from the reg to just above the top of the frame rail. Use two strap clamps on the two reg lines to bolt to the sheet metal just above the frame rail with a single hole for a 1/4-20 bolt and nylock nut. Both clamps share the single bolt.

The pressure gauge can be mounted directly to the regulator with a npt reducer. I'd put a filter after any diy fabbed line since the lip of the diy flare (if not double flared) can sometimes cut a little rubber off the inside that can hold the needle and seat open, flooding the motor.

I would have used a 4-6psi mech pump or electric at/in the tank and eliminate the need for the regulator.

Less rubber.jpg
 
70SwingerGuy said:
I use the same Holley dead head reg also, but I dont run a return line, that reg isnt made for one. Holley does make the same reg with a provision for a return line, it would make a much cleaner install if you go that route and keep the return line.
This is how I do mine, 6AN from mechanical pump to reg on inner fender, 6AN routed under the alternator and up to the fuel filter, gauge, then to carb.
Yes, I know I need to neaten the wires by the valve cover :lol:

View attachment 1716426165
View attachment 1716426166
View attachment 1716426167
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I added A WIX filter/vapor separator and the vapor lock issue disappeared
 
On the avatar 408 Demon, I run NiCu (nicop) line under the car then come up to my regulator as shown. This minimizes engine compartment heat to the fuel. Then I go over to the carb (850 Holley) with a braided Kevlar flex hose. The small NiCu line running under the cowl/firewall seam goes to my fuel pressure gauge on the cowl.

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MV8 said:
If all you want to do is run less rubber, another option is to run hard line on the chassis down to the frame rail then use short hoses at the rail for engine movement. Use common brake inverted flare to npt fittings on the regulator. Fit prefab ags steel or fab nicopp lines to run down from the reg to just above the top of the frame rail. Use two strap clamps on the two reg lines to bolt to the sheet metal just above the frame rail with a single hole for a 1/4-20 bolt and nylock nut. Both clamps share the single bolt.

The pressure gauge can be mounted directly to the regulator with a npt reducer. I'd put a filter after any diy fabbed line since the lip of the diy flare (if not double flared) can sometimes cut a little rubber off the inside that can hold the needle and seat open, flooding the motor.

I would have used a 4-6psi mech pump or electric at/in the tank and eliminate the need for the regulator.

View attachment 1716426185
Click to expand...
The issue I’ve found for small blocks is pumps that are adjustable and compatible with 3/8 fuel line are difficult to find. I spent weeks trying to source one through Mancini, Edelbrock, and Carter. The fuel pump that came with the 340 used 5/16” lines and was 5.5-6 PSI. Only the Hemi and the big blocks came stock with 3/8 line. At WOT 8-11PSI is fine, but Carters and holleys for the most part are rated for 5.5-6 PSI. An electric pump would probably be ideal, and in the end I may go there.

You are correct though, immediately I need to go to the gauge on the regulator route!
 
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Demonx2 said:
On the avatar 408 Demon, I run NiCu (nicop) line under the car then come up to my regulator as shown. This minimizes engine compartment heat to the fuel. Then I go over to the carb (850 Holley) with a braided Kevlar flex hose. The small NiCu line running under the cowl/firewall seam goes to my fuel pressure gauge on the cowl.

View attachment 1716426241
View attachment 1716426244
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Are you using a electric fuel pump?
 
Plymouth Pete said:
Man, chasing vapor lock is like playing Whac-A-Mole with a wrench. You fix one thing and something else pops up. Classic Mopar life
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I used a WIX filter/vapor separator and the vapor lock issue vanished. I tested it on a 96 degree Colorado day and allowed the engine to heat soak.
 
70SwingerGuy said:
I use the same Holley dead head reg also, but I dont run a return line, that reg isnt made for one. Holley does make the same reg with a provision for a return line, it would make a much cleaner install if you go that route and keep the return line.
This is how I do mine, 6AN from mechanical pump to reg on inner fender, 6AN routed under the alternator and up to the fuel filter, gauge, then to carb.
Yes, I know I need to neaten the wires by the valve cover :lol:

View attachment 1716426165
View attachment 1716426166
View attachment 1716426167
Click to expand...
Nice Demon!
 
I'm in the process of re-doing my fuel system on one of my cars, changing from an AFB to a holley.
I'm using the black fuel log for the holley.
The blue fitting came off the car with the Carter. It screwed directly into the regulator (3/8 npt) and enabled a small pressure gauge (1/8 npt) to be mounted directly. Other end is for the -6AN (red/blue fitting).
I dont know if the same thing is available for hard line or a rubber hose barb.

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