I have a 1985 F150 with a 302 V8 w/ 2bbl carb. This truck sat for like 6 years without being started up.

I have put in a new tank and fuel lines and the mechanical fuel pump wasn't sucking gas out of the tank. The guy at Napa convinced me to install a Posi-flo electric fuel pump... which is designed to go with carbureted engines. It works fine, but the way I have it wired up, whenever the ignition switch is in the "On" position... the pump is on and pumping. If the engine dies (as I have been experiencing here recently while reinstalling my newly rebuilt carb and trying to get the idle set properly)... that pump keeps pumping gas and it spills right out of the carb until the key is switched off.

The instructions strongly recommend wiring it into an Oil Pressure sensor circuit. I didn't know how... so I just used a circuit tester and found a wire under the hood that was hot when the the Ignition was On and spliced into that wire.

Can anybody advise on how I could better rewire this thing? Or maybe I should just scrap it in favor of putting in a new mechanical fuel pump like the truck was designed for in the first place? What say you?
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What is the output pressure of the pump? The fuel should not be pouring out of the carb with the pump running. Either the output pressure of the pump is way too high, or you have a problem with the carb. For a carburated application, you only need about 3 to 4 psi fuel pressure. Anything over 7 psi or so is probably beyond the limit of what the inlet needle valve can handle.

If the fuel is pouring out of the carburetor with the pump running and the engine off, it is likely also doing that with the engine running. The amount of fuel consumed by an idling engine is a microscopic portion of what the fuel pump can put out. Having the engine running is not enough of a fuel draw to keep the carb from overflowing.

It is a good idea to power the fuel pump through a safety switch so it only runs when there is oil pressure. Several companies sell switches for this purpose.

 

F100Jim - Thank you for your thoughtful response! The pump I installed is 4 - 7 psi... 35 GPH. I don't know crap about pumps. Maybe I should just buy a replacement mechanical fuel pump and chalk this up to a lesson learned? Seems like much of what I have learned about fixing cars has come as a result of me screwing up and spending money... so nothing new there.

 

I found an adjustable "Carbureted Fuel Pressure Regulator"... which seems like it would give me the ability to keep the fuel pressure dialed down to 5 PSI... Of course, it is $90+ bucks... And putting a mechanical one back in would probably just run me $38.00.

Aeromotive 13205 - Aeromotive Carbureted Adjustable Fuel Pressure Regulators - Suggested Parts - SummitRacing.com

Somebody jump in and let me know if all this modification away from the way God and the Motor Company intended the fuel to be pumped on this vehicle is just a bunch of foolishness. You won't hurt my feelings. Are there any pros to leaving this electric pump installed? Would this be considered an "upgrade" or just foolishness? Chime in fellahs!

 

Go back with a new mechanical pump that matches what the original pump was and you
will be much happier with the result. It should do the job fine.

 

Old Hickory I'm thinking you are right. I do have one concern though. The point made by F100Jim... about the PSI. When I look at the PSI rating on a replacement mechanical fuel pump... Autozone lists it as 5.5 to 9 PSI. Which is in the same ballpark as the electric one.

Given that my carb is overflowing gas... and apparently PSI may not be the issue... Now I'm wandering if I goofed on my carb rebuild in some way?????

 

More to the story... I spoke to a mechanic friend of mine about the issue and learned a little more that I thought I'd share. Turns out the issue of gas continuing to pump and overflow the carb after the engine stalls is not a function of the electric pump being wired up wrong. It is a result of my recent attempted rebuild of the carb most likely. As the bowl fills with gas, the float in the carb should lower that needle and close off the fuel inlet passage. My mistake was putting the carb back together and not bothering to do any adjustments to the float/the choke/the fast idle cam, etc. The Engine oil pressure safety switch I mentioned is really more of a safety feature in the event of an accident... in normal operating conditions, as mentioned above, the float in the carb would shut off the gas flow and when the pressure built up to a certain level in the fuel lines the pump will shut off on it's own. His opinion is the electric pump that's installed should work just fine after I solve my carb float issue.