Fuel return feed

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Nitro
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Fuel return feed

Post by Nitro » March 17th, 2007, 2:09 pm

Hi
I have 1500 SOHC Fiat X1/9 with twin 40 Webers (downdraught).
I have recently fitted a Facet silvertop electric fuel pump (4-4.5psi) installed inline with the mechanical pump.

My question is should there be or is there a need for a fuel return back to the tank?

It hasn't had one since I've owned the car but I was a bit concerned that this may be detrimental to the performace or longevity of componants.

If it needs one do I just T off the feed to the second carb?

Many Thanks

Graham

Guy Croft
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Post by Guy Croft » March 17th, 2007, 2:22 pm

Please clarify. Two pumps?


I have recently fitted a Facet silvertop electric fuel pump (4-4.5psi) installed inline with the mechanical pump.

GC

Nitro
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Post by Nitro » March 17th, 2007, 3:46 pm

Rather than bypass the existing mechanical pump I installed the Electric pump in line between the fuel tank and the mechanical pump.

Why did I do it that way?

To be honest for ease as I wasn't sure how to blank off the mechanical pump. It may have an advantage that if the electric one fails for any reason the mechanical one will still work (trying to justify myself)

Graham

Guy Croft
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Post by Guy Croft » March 18th, 2007, 5:54 pm

Well, I think that I'd be tempted to run just the one. I guess I should know what happens for sure if you run 2 pumps in series but I'm not sure. maybe doubling of pressure? I have never done it!

The best thing to do if you don't have the means to make a fuel pump blank plate is run a single Facet mounted in the boot ie: pushing not pulling, and disconnect the lines from the mech one. No regulator is needed with the Silver Top, an in-line filter like FSE's Purolator is a good idea but to be honest there are many to choose from and with a carb it doesn't need an Olympic standard of filtration. The Silver Top takes a high current and really needs heavy duty cabling like the black earth cable attached to it - and preferably should be activated either from the ignition positive supply via a relay, or with a separate feed via a dasboard switch. Both must be fused..

The Silver Top pressure will not lift the float needle off its seat and no it doesn't have to have a fuel return line. This is something really only needed with mechanical pumps - because they create low pressure in the line from tank to pump and the fuel can boil at altitude on hot days. Boiling of the fuel in the float chamber stop the engine running at all. The return line circulates the fuel to help preven that.

GC
Last edited by Guy Croft on March 20th, 2007, 8:41 am, edited 1 time in total.

Nitro
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Post by Nitro » March 20th, 2007, 8:14 am

Thanks for the advice.

Graham

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