How to plumb a closed loop fuel system on webers

[John Z]

Gents,

I currently run Weber IDAs on a Gurney 302. I obviously have 2 fuel pumps. Both have check valves that feed a regulator. I have one fuel line running from the regulator to the carbs which are all connected in a closed loop. My car is percolating REAL bad after shut down when it’s hot. So bad, it leaking out of the throttle shafts on all 4 carbs into the tray. My engine builder suggests installing a return line to help drop the pressure when the car is shut off.

Does anyone have a simple schematic of a closed loop fuel system with a return? I would like to add the return with minimal disruption as the system is currently plumbed very well.

Thanks for any help you can provide.

Z

 

[Mark H.]

I had a Cobra with the same issue. I would just shut off the fuel pumps prior to shutting down the engine. Let it idle for 15-20 or so seconds, then cut the ignition. This drains the bowls, so no percolating. Always got a nice restart, hot or cold (with pumps back on).

 

[Frank Catt]

Gents,

I currently run Weber IDAs on a Gurney 302. I obviously have 2 fuel pumps. Both have check valves that feed a regulator. I have one fuel line running from the regulator to the carbs which are all connected in a closed loop. My car is percolating REAL bad after shut down when it’s hot. So bad, it leaking out of the throttle shafts on all 4 carbs into the tray. My engine builder suggests installing a return line to help drop the pressure when the car is shut off.

Does anyone have a simple schematic of a closed loop fuel system with a return? I would like to add the return with minimal disruption as the system is currently plumbed very well.

Thanks for any help you can provide.

Z

Z I have successfully used a solution to this for many years, simple install and immediate full pressure dump as soon as engine stopped , Frank

 

[John Z]

I had a Cobra with the same issue. I would just shut off the fuel pumps prior to shutting down the engine. Let it idle for 15-20 or so seconds, then cut the ignition. This drains the bowls, so no percolating. Always got a nice restart, hot or cold (with pumps back on).

Thank you!

 

[John Z]

Z I have successfully used a solution to this for many years, simple install and immediate full pressure dump as soon as engine stopped , Frank

Frank, thanks for your reply. What’s the solution you reference?

 

[JP Verweij]

You can run a double banjo on the last carb.
The second banjo (return) needs a .5mm restriction inside before it goes back to the fuel tank.
This is how I do all my builds. Engine off, pressurised fuel bleeds off to the fuel tank.

 

[John]

Some of the original cars had the fuel dump just after the Fispa filter. You can install an AN fitting 'T' in line. Obviously the drain is a smaller diameter 'restriction' fuel line heading back to the tank as JP and Frank mentioned. As long as you still have approx 3psi at your carbs when running,...when you kill the pumps the residual pressure will drain off.

 

[Frank Catt]

Frank, thanks for your reply. What’s the solution you reference?

Send me an E on [email protected] and I will describe.

 

[John Z]

You can run a double banjo on the last carb.
The second banjo (return) needs a .5mm restriction inside before it goes back to the fuel tank.
This is how I do all my builds. Engine off, pressurised fuel bleeds off to the fuel tank.

Thank you!

 

[Walter]

or, for a more controlled fuel return, use a pressure valve of suitable value (~ 4 psi) in the return line to the tank - Kinsler can supply. I use one of them to avoid over-pressuring the fuel swirl pot in an EFI system.

 

[Ian Clark]

Hi John,

You're a lucky man to have identified the issue when it was only percolating. Again many great suggestions from the GT40s Forum to consider for your GT40

The primary issue however is not the plumbing, it's the underhood temperature. The heat soak is exrtremely high given there are no cooling fans or adequate ventilation for standing heat in the engine bay of a GT40 parked hot in high ambient temperatures.

Depending on the day these are a couple of options to prevent fuel boiling turning into something much worse:

Open the rear clamshell and let the onlookers be amazed!

Turns off the fuel pump(s) some time before eather reaching your parked location or idle it dry once parked

If you want to put a lot of hours into it you could replicate an original style Ford GT40 rear mounted condenser/cooling fan assembly as per the three original A/C equipped Ford GT40s or the first hundred (or so) CAV GT40s. The A/C condener fan runs after ignition off like your rad fans

Always a good idea to keep an up to date fire extingisher in the cockit and hope you never need it

Cheers
Ian

 

[Mark H.]

Hi Ivan, would you have any pictures of the A/C fans you spoke of in the original 40's or know where I could look? Can't find any internet info on these. Thanks

 

[John Z]

Hi John,

You're a lucky man to have identified the issue when it was only percolating. Again many great suggestions from the GT40s Forum to consider for your GT40

The primary issue however is not the plumbing, it's the underhood temperature. The heat soak is exrtremely high given there are no cooling fans or adequate ventilation for standing heat in the engine bay of a GT40 parked hot in high ambient temperatures.

Depending on the day these are a couple of options to prevent fuel boiling turning into something much worse:

Open the rear clamshell and let the onlookers be amazed!

Turns off the fuel pump(s) some time before eather reaching your parked location or idle it dry once parked

If you want to put a lot of hours into it you could replicate an original style Ford GT40 rear mounted condenser/cooling fan assembly as per the three original A/C equipped Ford GT40s or the first hundred (or so) CAV GT40s. The A/C condener fan runs after ignition off like your rad fans

Always a good idea to keep an up to date fire extingisher in the cockit and hope you never need it

Cheers
Ian

Thanks Ian!

 

[Frank Catt]

John, I have to disagree with above, not the solution that is safe ! Frank