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GT40 Tech - Fueling, Electrics, & Engine Cooling Petrol, Electrons, & Water

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Old 13th August 2017, 04:03 PM   #1
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Fuel System Reconfiguration

The original builder/owners of this car took an interesting, but less preferable approach for the twin tank fuel system.

Each tank has a dedicated pump, filter, regulator and gauge feeding one bank of cylinders. This means both pumps need to operate full time. See attached system diagram.

Additionally, each QFT regulator has one output port connected to tank return with what appears to be a restrictor of some kind. I assume this was done to prevent the Carter P4070 pumps from deadheading at the regulators, but I think the net result will be to lose pressure at the carbs when under heavy load. To test my theory, I disconnected the LH drain at the regulator and capped it off. When I ran the pump, the gauge ran up to 5.5 PSI, rather than 3 PSI as previously set. This tells me that at least 2.5 PSI is bleeding off at static load.

So my plan now is to place a one way check valve in each pressure line (probably where the gauges are located), connect the two capped off fuel bars (dashed line in diagram with one gauge in the middle) to complete the pressure path, and cap off both drain lines. Anyone see a reason why this wouldn't resolve the problem and allow me to run from either tank?
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Fuel System Reconfiguration-slide1-jpg   Fuel System Reconfiguration-dscn1784-jpg   Fuel System Reconfiguration-dscn1785-jpg   Fuel System Reconfiguration-dscn1793-jpg  
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Old 5th September 2017, 06:07 PM   #2
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Re: Fuel System Reconfiguration

Hi Mike,
Short of dismantling and re-engineering your system to a reservoir tank to feed the carbs I don't see why your idea can't work with one critical caveat. The Weber's float bowl valve seat are very sensitive to pressure, get it down to 3psi. 5psi will force the valve to raise the fuel level in the float bowl and cause issues. I found the regulators like you show in the pictures are inadequate to reduce the pressure to an accurate 3psi setting and need to be modified. Up until now modification to the regulator was necessary to achieve a low setting but Automotive now sells a regulator that you can adjust to very low settings.
In addition, Pierce Manifolds sells a Weber specific fuel pump that pumps only 3psi.
Tim
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Old 5th September 2017, 07:55 PM   #3
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Re: Fuel System Reconfiguration

Hi Tim,

Thanks for replying. I plumbed the system as per my diagram and I can now run the engine from either tank, but I came to the same conclusion that the QFT regs cannot reliably maintain 3 psi. I disconnected & capped the drains, but pressure stability is only marginally improved.

I've been down this road before running 48 IDFs on my cobra. Holley makes a 12-804 low pressure regulator (1-4 PSI) which works well for this application and apparently QFT makes a comparable model (30-804). I was hoping the previous owner went with the correct model, but apparently not. Guess I'll be buying two new regs. About $27 each, but quite a bit cheaper than two new low pressure pumps from PM.

Mike
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