1970 911T fuel pump for Zeniths?

[924CarreraGTP]

Hello Pelicans, my name is Justin and I live in Arkansas. I have a 1970 Porsche 911T with Zenith 40tin carbs and NO rust with the original (rebuilt) 2.2. The fuel pump is possibly the original pump with 3 spouts. I'm understanding this is one in, and two out including a recirculation back to the tank? I cannot afford the $699 for the original pump but Advance Autoparts in my town has an Airtex inline fuel pump for the 1970 911T. Have any of you adapted an inline pump and what kind of advise can you give me for it? I understand the Zeniths only need 4psi to run the car.
I am considering blocking off the recirculation into the tank but I'm not sure if this is what I need to do.
How do I handle this situation? I know its best to fit a Porsche with original parts as I have an '84 928S and an '85 944, but I'm simply trying to get this car to run.
Also the starter turns over and will not stop from time to time. Any ideas on this?
Thank You,
Justin

[James Brown]

You are describing a high pressure fuel injection pump with a bypass. A holly pump or a low pressure pump dead heading (without the bypass) is fine. pressure needs to be around 3 psi at the carbs. Volume is also important, don't have the spec now. the starter solenoid might be sticking due to the contacts always arcing causing small pits witch sometimes interlock causing the contacts to stick. Replacing the solenoid should fix this.

[mcaterino]

I just restored a 1970 T, with more or less the original engine (upgraded to 2.4 through longer stroke), running Zeniths. The car came with the original fuel pump as you describe, mounted behind the steering rack and with a return to the tank. But it was ancient and in unknown condition. So on the basis of a number of posts here I bought the Pierburg pump (901-608-106-00-M244, from Pelican of course). It does not have a fuel return, just an input from the tank and output to the tunnel fuel line. I plugged the tank return input. It works fine. I suppose someone will chime in to let us know the importance of having the return in place, but it doesn't seem to cause me any trouble.

Mike

[924CarreraGTP]

Can anyone tell me the reason for the fuel return line? Was it for recirculation or for pump cooling? The pump is certainly ancient along with the fuel hoses. What was the purpose of the return line on a carburetted car?

[ratpiper71T]

Can anyone tell me the reason for the fuel return line? Was it for recirculation or for pump cooling? The pump is certainly ancient along with the fuel hoses. What was the purpose of the return line on a carburetted car?

Here's a thread that can answer that question. Not a bad idea at all if you live in a hot climate.

Weber fuel recirculation- Questions

And another

Fuel return lines 71T?

[Joe Bob]

Recirculation is a good idea.....keeps things cool and is easier on the pump. Why change?

[Grady Clay]

Justin,
First, WELCOME to Pelican
You will find a lot of help here
(including 928 and 944 on other forums)

Yes, temporarily install an appropriate inexpensive pump that will provide about 4.3 psi.
You can temporarily block off the return.
Be sure to check the pressure at the carburators and the open flow rate in a hose back to the tank or a container.
Have a BIG CO2 fire extinguisher handy.

Your running Bosch pump can be ‘rebuilt’.
Probably cleaning and new O-rings will do.
There are several threads on this.
This is a VERY good pump.

It is very common for the screen filter to be restricted with fuel tank debris.
This is part of the outlet fitting screwed into the fuel tank.
I recommend you remove the fuel tank, remove the fittings, fuel level sender and clean the tank.
You will see the filter screen restriction.
Be gentle with the brass screen.
If the screen is damaged, replace it with the original brass part and not the plastic VW-914 version.

Replace all the fuel hoses with new OEM (available from our host) hose.
Be sure to use the original Norma-Schellen (N-S) type clamps and not screw-type.




There are two Bosch electric pumps that appear identical, a low-pressure one for the 911T carburetors and a high-pressure one for 911E and 911S MFI.

For the 911T carbs:
Porsche part number – 911.608.107.00
Bosch part number – 058096 0009
Operating Pressure – 0.3 bar (4.3 psi)
Pressure relief valve opens from – 0.2-0.3 bar (2.8-4.3 psi)
Fuel delivery capacity – 80 liters per hour
Current draw – 2.5 A @ 12 V
RPM – approx. 2000 rpm


For the 911E & 911S MFI:
Porsche part number – 901.608.105.00
Bosch part number – 058097 0001
Operating Pressure – 1.0 bar (14.2 psi)
Pressure relief valve opens from – approx. 2 bar (28 psi)
Fuel delivery capacity – 125 liters per hour
Current draw – 3.5 A @ 12 V
RPM – approx. 2800 rpm

The 911T pump pressure relief is the pressure regulating mechanism.

The 911E&S pump pressure relief is a safety pressure relief.
The MFI pressure regulation [0.8 ±0.2 bar (11.8 ±0.3 psi)] is done with the return fitting at the fuel console.
The safety pressure relief partially opens to allow fuel to the filter, exercising the safety while running.



Mike and Justin,

I want to know if your cars have the MFI fuel return pipe in the tunnel.
If there (I think it should be), it should have a little rubber cap on each end and probably filled with heavy grease.

One of the best things we can do for our carbureted cars is to plumb the system for fuel circulation past the carb inlets and back to the tank.
Having as many fuel components (pump, filter, pressure regulator, etc.) at the front keeps the fuel cool.
Insulating the hoses from the tunnel to the carbs is also critical.
…As are insulators between the heads and intake manifolds.


I didn’t realize I had posted an incomplete diagram on the thread linked above: Weber fuel recirculation- Questions
I’ll fix that.
Here:
EDIT

]



1) Fuel tank.
2) Filter screen fitting in tank.
3) Electric fuel pump with check valve.
4) Fuel filter.
5) Supply hose & pipe (7 mm, -6 size).
6) Tee fitting on supply side.
7) Double banjo fittings at carbs (4 total).
8) Tee on return side with pressure/sample port.
9) Return hose & pipe (9 mm, -8 size or larger).
10) Fuel pressure sender.
11) Fuel pressure regulator with bypass restriction.
12) Tee for pump relief (if used).
13) Return fitting to tank.



The ‘run-on’ with the starter can be either in the ignition switch or starter.
I recommend you get a new Bosch rebuilt starter and be done with that possibility (old starters are a pita).

Best,
Grady

[PropellerHead]

Justin,
Welcome!
You'll find Grady's advice to be 'gospel' around here. He's spot-on.

If you go the temporary route with an in-line 'universal' type pump, you will need a pressure regulator too. Get an adjustable unit so that you can ensure the pressure at the carbs is where it should be (i.e. you'll want a gauge too). To keep the pump from dead-heading (which may cause it to burn up) and to keep the fuel pressure regulated properly you need a return flow path. The original unit does all this internal to the pump.

[924CarreraGTP]

I understand the issue with recirculation but here is my next question. To save weight and complexity, what about a 3 way fuel pressure regulator in line at the pump up front? That way the third leg can be pumped back to the tank just like the original pump did. Will this work or am I more dense than I give myself credit for?
Thanks Grady for the diagram. It helped greatly to see how the system works. Though I have one more question. In my car there is a canister where the battery goes up front that looks to have fuel line and liquid inside it. What is this dohicky?
I always thought the 928 was a space ship compared the 914 I used to have, but this 911 is pretty complex for it's age.