SPF P2306 Fuel Pump Configuration Question

Maybe this will be an easy answer ... I came from CAV to SPF and I am accustomed to dual fuel pumps. But ... 2306 has me confused. It has two Carter bulkhead mount electric pumps in series pulling from the left tank. One is in the left sill pocket and one is on the firewall. There is only a -12 AN crossover line from the right tank feeding the left tank. The layout is thus:

left tank > filter > pump 1 > swirl tank | > pump 2 > press gauge> carb
-------------------------------------------V
-------------------------------------left tank return

Is this a typical SPF layout? I've never seen two pumps in line like this. I'm fine with the single tank feed, nothing to toggle.

The return is off the swirl tank before pump 2. Line dead heads at the carb. Notice there is no pressure regulator! I am about to remedy that. This was a balls out track car, maybe the orig owner wanted lots of pressure at the carb. But it shows 14 psi at the gauge and I think that caused me to flood out the other day. Quick Fuel says they like 7 psi at the carb. Restarted ok and I continued my trip. Anything jump out that might be wrong here?

Sam
 

Neil

Supporter
There is no good reason to put two Carter fuel pumps in series. In series the fuel pressure is additive (7psi + 7psi = 14psi as you noted). Without a fuel pressure regulator, this high pressure will force the inlet needle off its seat and flood the engine. If you put the two fuel pumps in parallel, their fuel flow is doubled and the pressure is still 7psi. You really don't need the extra flow and the current draw is doubled (more or less) so one Carter rotary pump is all you need. One reason to keep the extra pump mounted in place but not used would be to have a spare in case of emergency.
 
There is no good reason to put two Carter fuel pumps in series. In series the fuel pressure is additive (7psi + 7psi = 14psi as you noted). Without a fuel pressure regulator, this high pressure will force the inlet needle off its seat and flood the engine. If you put the two fuel pumps in parallel, their fuel flow is doubled and the pressure is still 7psi. You really don't need the extra flow and the current draw is doubled (more or less) so one Carter rotary pump is all you need. One reason to keep the extra pump mounted in place but not used would be to have a spare in case of emergency.

Thank you Neil. What do you think about the tank return from the swirl tank, as opposed to the end of the fuel log? Should I plumb around the spare pump, or will it pass fuel freely?

Sam
 
Ask the installer what they were doing. This is not "SPF" as they don't do the pumps, this is pure installer.
Rick, yes, I intend to call Dennis and pick his brain this week. But I usually learn a lot from the other owners on this forum so I thought I'd ask. Just read the stiff throttle cable thread above ... been fooling with that for months :rolleyes:
 

Neil

Supporter
Sam;

Disconnect the hoses to/from one fuel pump and plug the fittings to keep out dirt and break the wiring to it or install an on/off switch in that line. I have no opinion on the fuel return line; either should be OK.
 
Sam;

Disconnect the hoses to/from one fuel pump and plug the fittings to keep out dirt and break the wiring to it or install an on/off switch in that line. I have no opinion on the fuel return line; either should be OK.

Got it, thanks again Neil!

Sam
 

Ron Scarboro

GT40s Supporter
Supporter
Maybe this will be an easy answer ... I came from CAV to SPF and I am accustomed to dual fuel pumps. But ... 2306 has me confused. It has two Carter bulkhead mount electric pumps in series pulling from the left tank. One is in the left sill pocket and one is on the firewall. There is only a -12 AN crossover line from the right tank feeding the left tank. The layout is thus:

left tank > filter > pump 1 > swirl tank | > pump 2 > press gauge> carb
-------------------------------------------V
-------------------------------------left tank return

Is this a typical SPF layout? I've never seen two pumps in line like this. I'm fine with the single tank feed, nothing to toggle.

The return is off the swirl tank before pump 2. Line dead heads at the carb. Notice there is no pressure regulator! I am about to remedy that. This was a balls out track car, maybe the orig owner wanted lots of pressure at the carb. But it shows 14 psi at the gauge and I think that caused me to flood out the other day. Quick Fuel says they like 7 psi at the carb. Restarted ok and I continued my trip. Anything jump out that might be wrong here?

Sam

This is not a particularly atypical set-up.

Pump 1 is filling and maintaining the Swirl Pot. This solves cavitation on cornering and braking.
Pump 2 is drawing from the Swirl pot and feeding the engine.

The Swirl Pot will be at minimal pressure if any at all.
The Right / Left tanks will equalize from the crossover.

If you have two pumps representing "Pump 2" then it is for looks and the regulator is keeping the pressure down to an appropriate level.
 

Ron Scarboro

GT40s Supporter
Supporter
OK, so I read more carefully. You shouldn't be running 14psi at the carb. If you put a regulator between Pump 2 and the carb, you'll be fine.
 
OK, so I read more carefully. You shouldn't be running 14psi at the carb. If you put a regulator between Pump 2 and the carb, you'll be fine.

Ron, this is where I think I am headed. I did get hold of Dennis this am and he confirms what you said about the swirl pot. The pumps are not additive because the swirl pot is also dumping into the 0 psi tank return. But he thinks pump 2 is a 7 psi pump and he's mystified as to why it is making 14 psi. He suggested disassembling the pump to inspect the ball valve regulator. Repair or replace pump 2 and if it is making 7 psi, a regulator is redundant. Also, he suggested changing the gauge, as they are unreliable. Somewhere here is the answer, waiting for me to try some things ... Thanks!

Sam
 

Ron Scarboro

GT40s Supporter
Supporter
I'm a fan of regulators. It just gives you more than a single point of failure. Easiest thing IMHO is to put a good ol' Holley unit regulator in the system.

My $0.02 priced for value.

Best,

Ron
 
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