'74 400 oem Thermoquad Fuel Pressure?

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Old 03-06-2010, 05:41 PM
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'74 400 oem Thermoquad Fuel Pressure?

Well... I finally did it. I bought an electric fuel pump for the wagon. My dad always talked about installing one and that started in 1976 when the car was two years old. It's 36 years old now but only has 55,000 miles on it.

This thing has always been hard to start. Ignition system (distributor, pickup, coil, 12 vdc plus during cranking, amplifier, wires, plugs etc) perfect, no vacuum leaks, High efficiency starter with low amperage draw, NEW oem style Thermoquad with working electric choke, fuel lines clear, vented cap, several new mechanical pumps and it still cranks forever before I get fire. Pumping the snot outta the accelerator doesn't do much.... Cold after sitting is the worse case scenario.

What's always made me think fuel delivery problem is that it cranks for 30-45 seconds after sitting for a week or more, 15-20 seconds after a couple days and 5-10 seconds if it was run the day before. I have a high end Bosch mechanical pump on it now and the check valve works....

So... found a new Holley style electric pump today from a friend for really good price and bought it. It's rated 140 GPH (!) and 9 psi.

I have not yet looked at my old factory manual for fuel pressure numbers that the T Quad likes but is 9 psi too high? Seems like 7-8 psi is the sweet spot.... Before I add a regulator I'll probably bench test the dead head pressure from the new pump.

Also.... do I HAVE to install a bypass type filter and return line?

Anyone have any input on this?

Thanks,

stilbo

Last edited by stilbo; 03-06-2010 at 05:44 PM.
Old 03-07-2010, 08:17 PM
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about 7 PSI sounds right; much more and you'll be blowing the needle off the seat overpowering the float;
Old 03-08-2010, 02:23 AM
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Thanks!
Old 03-08-2010, 04:08 AM
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yeah. 5 to 7 max lbs. The less you can get away with the better. With a carb, flow is more important than pressure. Might also want to consider some type of emergency cut off switch for that electric fuel pump. (like a ford rollover valve0
Old 03-08-2010, 08:04 PM
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Wow... Thanks for the advice on the Ford Inertia Switch!

That's an easy salvage yard part too!
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