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Mechanical Fuel pump return line ?

 
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AlsCustomS



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PostPosted: Sun Jan 01, 2017 9:25 am    Post subject: Mechanical Fuel pump return line ? Reply with quote

Doing some reading on the subject of different fuels in different states and temperature, causing fuel boil and vapor lock on some carbs.
The cure seems to be a return line tee in front of the carb 1/16 outlet on the tee back to the tank, to keep fuel cooler.
Antone try this ? changing the rear end on my 69 and while there is room to run a return line was giving it some thought.
Thanks for your time,
AL Question

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Larry
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PostPosted: Sun Jan 01, 2017 10:38 am    Post subject: Fuel Return Line Reply with quote

There seem to be a lot of differing opinions on a return line to the tank. It appears that it would be best to use a regulator that has a pressure setting which will allow fuel to return if the pressure goes up, such as at idle when less fuel is needed and the pump keeps pumping (especially if your pump is over the 5-7 psi recommended for carb cars). However, all electric pumps I have used shut off as the pressure was reached (even if only "clicking" more slowly). If you have an electric pump that runs constantly (like a Holley one I once had that burned up in just a short time), perhaps a return line is needed.

I don't see how a line with even a small hole in it (the return) will allow for proper fuel pressure; hence a regulator needed.

You mention a '69. My '69 Lemans had the return line at the mechanical pump back to the tank. Yours not have one?

Unless you're doing some super power setup, I would just go with whatever was stock. Down here in Florida, where it can be a million degrees in the summer, we still don't have any vapor issues except for the very old cars... but they always did wherever they were at. Any problem might be solved with a little heat wrap on the fuel line.

I'd like to hear other thoughts.

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AlsCustomS



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PostPosted: Mon Jan 02, 2017 10:52 am    Post subject: Reply with quote

I got under the hood and found what looks to be a return line on the fuel pump plugged off.
A new tank was installed on the car before I bought it and can't find a return line on the frame.
The previous owner ran a 5/16" rubber fuel line from tank to fuel pump, I'll be running it in steel while under it. No idea where to run return off pump at tank ?
I will check fuel pressure soon first.
Project S by the way is a rear end I found from a 68 lemans with a 3.08 open, transformed with all new Yukon 3.36 posi parts and axles with drilled disc braking kit And 17" wheels BF Goodrich G force comp 2 tires, and all new tube suspension upper shock mount and frame braces 1' shorter springs and a whole lot more going on front.
I'm pretty exited to have the best handling convertible out there !

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Larry
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PostPosted: Mon Jan 02, 2017 12:33 pm    Post subject: Tempest Fuel Tank/Vents Reply with quote

I had to do some thinking and double checking about my '69 Custom S wagon. Yes, mine has a steel vapor return line at the fuel pump. And it also had other vents. However, I have removed the side tank and installed a fuel cell, so none of the above is being used. Note from the photos mine is "a little" modified. When finished my '40 will get back to work on it.

However, check the illustrations below from the '69 Shop Manual; I'm sure the '68 is the same.

As on my wagon, the vapor return line was on the fuel sending unit- don't get them mixed up... I've heard bad reports about that.

Note that you tank also has some sort of front vent as well as a rear vent on the filler pipe.

Hope this all helps.

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