Fuel Pump gurus: Questions about my 71 T

[Alan.UK]

Hi all,

I have a few quick questions that I hope someone can help me with.

1. When was the fuel pump moved from under the tank to the rear of the car ?
2. My 71 T (US car) now has webers but I persume it would have had zeniths, correct ?
3. Did all cars that run zeniths have a fuel return line to the fuel tank ?
4. Do zeniths run on the same PSI as webers ? are the fuel pumps the same?
5. Is there any issues with running a factory carb fuel pump at the rear of the car to run some larger 46mm carbs ?

Thanks in advance

Alan.UK

[jpnovak]

The fuel pump was moved on some mfi cars in 72-73. I have seen them in both places but mostly in the rear.

The 71T likely had Zeniths from the factory

All carb'd and MFI cars had a return line from the pump back to the tank

The factroy pump should be a Bosch Rotary style pump. They run forever and will work fine with webers or Zeniths. They will supply pleny of fuel if you want to run 46s.

Are you putting in a bigger engine? 46s will be way too big for a 2.2 unless its a track only car with really hot cams spending all its time at 6K+ rpm.

[Alan.UK]

Hi Jamie,

I have a 1971 2.2T that I am building a short stroke 3.2 for, which has 46 mm PMOs. I did think that this car had the fuel pump under the tank and hence thought I would have to run a return lines from the carbs back to the tank, as good practice.

Whilst taking the motor out yesterday I noticed that the fuel pump is actually just above the anti roll bar mount and it is still there with the return lines just blocked off. I did think this was not done until 72 so I was surprised.

Anyway I hoping that this saves me some work, as the pump there would have been for the zeniths and thus I can use it for my PMOs and also a return line is also already there.

Does anyone know if there are any issues with a fuel pump position at the back of the car supplying good constant fuel to carbs. If the set up I have is factory then there should be no problems ?


Fingers crossed the pump works ?

Thanks

Alan.UK

[jpnovak]

Both of my 71s had fuel pumps in the rear driver side on the widened sway bar mount. I have had no problems with fuel delivery. The ST is custom plumbed. I have an inline fuel pump going to a PMO distributor/gauge. This block splits off three ways, two for each carb bank and one for the return line back through the tunnel. I have a clamp on the return line to dial in the pressure to 3 psi. Works great.

[Grady Clay]

Alan,

I agree with Jamie.

1) ’69 & ’70 had the pump at the fuel tank mounted on the cross-member. IMHO the best location.

2) Yes, your ‘71T had Zeniths originally. They work just fine but are not as adjustable as the Webers for non-original applications.

3) Yes, the front mounted pumps have a pressure relief return directly to the tank. The rear mounted pumps had the same return, just down the tunnel. None of the Factory systems returned fuel past the carburetors (a deficiency IMO.)

4) Yes and yes. The pump is 0.3 bar (4.3 psi) where the pressure relief valve in the pump is spec at 0.2-0.3 bar (2.9-4.3 psi). This is the Porsche 911.608.107.00, Bosch 058096 0009 or supercedes electric fuel pump. It is rated at 80 liters per hour, 2.5A @ 12V, and about 2000 RPM.

5) The fuel flow capacity of a fuel pump is related to the fuel use of the engine (horsepower) and the amount returned to the fuel tank. I have used this pump with ~300 HP engines.

Today, I would use a system that passes the fuel past the carb intakes and returned the unused fuel to the tank while maintaining proper (~4 psi) pressure at the carb needle & seat. The issue is to keep cool fuel at the N&S so it doesn’t flash into vapor when the pressure drops across the N&S.

Best,
Grady

[Alan.UK]

Thanks for the info guys.
The set up I was planning to use is exactly as you describe Grady. That is how the kit from PMO works. Until yesterday I thought I needed a new pump and to also install a hard fuel return from the carbs l to the tank.

It seems lady luck is with me as the pump is already there (with original power supply) and the hard fuel return line is also there. Great...

Lets hope the rest of the work goes this smoothly.

Thanks again

Alan.UK