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PostPosted: Thu Mar 29, 2012 7:38 pm 
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Ditto. An electric fuel pump is good at pushing fuel. It isn't very good at pulling it. If the fuel pump is mounted too high above the fuel level, you could be starving for fuel.
Conversely, if the pressure is too high, not used in conjunction with an appropriate fuel pressure regulator, you could overpower the float needle in the carburetor and run rich, or worse, flood out the engine.

The mechanical pump is preferred for even low percentage street use. An electric pump adds complexity and additional failure possibilities. Not all electric pumps are created equal of course. Generally the good ones are meant to flow far more fuel than a slant six will ever need, and will be in bypass mode most of the time, which heats the fuel in the line by continuous pumping. Some will require a return, though I doubt that is the type your running.
The average inline fuel pump will be a solenoid type, which is noisy and short lived.
For racing applications, a mechanical pump is still a pretty good choice. The amount of power required to operate it is negligable. I doubt you would see it on a time slip.
If greater fuel delivery is needed, that could be a good reason to go with an electric pump. For a slant, that would require higher fuel flow than most cars are going to need. Any but E-85 or Methanol cars would likely not benefit at all.
The last vehicle I had that needed more than an OEM pump was a seriously pumped up Big Block. Fortunately, there was an industrial truck mechanical pump that provided adequate flow. Problem solved. Prior to that it would run out of fuel in the bowls of the double pumper making the shift from 3rd to 4th when I had my foot on the floor.

I run a Holley Red pump on the Hooptie. The cam core had a worn out pump eccentric. No other reason to do it.

CJ

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PostPosted: Thu Mar 29, 2012 8:10 pm 
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the mechanical pump he put on before the electric one wasnt getting fuel to the carb. he said he thought the eccentric was worn out. Now, with some of the dry rotted and rusted vacuum lines, could that have caused the lack of fuel to the carb? I'm way more lost now because the previous owner did say it had 40k original miles, and if its a worn out eccentric that wouldnt make sense.

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PostPosted: Thu Mar 29, 2012 9:06 pm 
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Ceej wrote:
If the fuel pump is mounted too high above the fuel level, you could be starving for fuel.
Conversely, if the pressure is too high, not used in conjunction with an appropriate fuel pressure regulator, you could overpower the float needle in the carburetor and run rich


…and if the installer powered it via the same circuit already feeding the ignition, that circuit is now badly overloaded and the ignition system and fuel pump alike are seeing less voltage than they want.


Quote:
or worse, flood out the engine.


Or even worse than that. Unlike a fuel injected application with a fully-closed fuel supply system, a carbureted application has an open fuel supply system. If you have a problem that causes the carburetor to flood (stuck float, stuck inlet needle, etc.), the engine will stall. A mechanical fuel pump will stop pumping, but an electric one will keep right on pumping as long as it has power; it'll pump the contents of your fuel tank into the carb, which will overflow and spill into the intake tract and onto the (hot?) engine and street below. The same will happen if you are in a serious crash. Sure, "turn off the ignition", but you have to think about situations in which you might not be able to do so. This can be addressed with thoughtful fuel pump control circuitry, but if it's not addressed at all, it's not safe. And the main relay for the pump needs to get wired with its trigger circuit contingent on the oil pressure sender's state. If there's a ground at the sender, then the pump doesn't operate. That way when the engine stalls for whatever reason, the fuel pump will quit running after oil pressure drops off (usually within a few seconds of engine shutdown). The smart installer also puts in an inertial cutoff switch that kills power to the fuel pump if the car is hit hard.

Properly putting in an E-pump also means looking at the charging system, which is pretty marginal and beleagured on many of our cars. Line voltage already drops at idle -- lights dim, heater fan slows, radio gets quieter and staticky, wipers slow down, and ignition quality gets poorer until the engine is revved up. Adding another steady load on the electrical system will aggravate all those symptoms as well as stressing the fuel pump motor (motors don't like undervoltage; it makes them run hot). This is not incurable, either; there are perfectly good upgrades to be made to the alternator and the charging system wiring. But like proper control circuitry, it adds to the cost and complexity of "just put in an electric pump".

An air leak (from rust or anything else) in the line from the fuel tank to the fuel pump can and will prevent fuel from reaching the (mechanical) fuel pump. So will a partial blockage anywhere in that line.

An old vehicle with only 40k miles is very likely to require attention to the entire fuel system -- clean the crud out of the gas tank and replace the filter "sock" on the end of the pickup pipe, inspect and repair the fuel lines, replace all the pieces of flex hose in the system with new (fuel injection rated), new fuel filter, etc. An old vehicle with only 40k miles is very UNlikely to have a worn-out cam eccentric.

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Last edited by SlantSixDan on Sat Aug 01, 2020 3:32 pm, edited 2 times in total.

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PostPosted: Thu Mar 29, 2012 9:24 pm 
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Location: York NE
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Mis-adjusted or sticky valves can cause backfiring and stalling as well. You might want to look at that. An engine that sat for a long time can have valves stick (ask me how I know. My 62 sat for 23 years before I bought it).

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1977 d-200 crew cab ex-army pickup wants it's /6 back
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PostPosted: Wed Apr 04, 2012 8:57 am 
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Ok, here's what I did this weekend. My alternator came in Saturday and i swapped it in. Boom. No more sputtering. I'm guessing that maybe the low voltage wouldn't run the inline pump? Anyways, with the vacuum lines I replaced and the freshly cleaned carburetor the van is running as well as it ever has. I plan on pulling out the inline pump and testing the mechanical pump soon to try to solve that, but that wont be for a little while yet. Thanks for the advice even though my meager slant skills couldn't do it justice. PS: I photocopied about 100 pages out of those books.

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