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Old 05-27-2005, 08:49 AM
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Priming the mechanical fuel pump

I'm trying to get my engine started and I have a question about the fuel pump.

I wanted to flush the fuel lines before hooking them up to my new Demon carb, so I cranked the engine (with the + disconnected on the distributor) for 10-20 seconds about 8 times and could not get any gas to feed through the lines.

I disconnected the inlet and outlets and even removed the pump to check it out and it all looks fine. I don't think there are any leaks on the inlet side either but haven't ran any pressure tests.

I know that with some non-automotive diaphram type pumps, they need to be primed to get going and I'm wondering if this is what's needed in my case.

This is a new engine, new pump, etc... and yes! there's gas in the tank!

Thanks!

Dan

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Old 05-27-2005, 10:11 AM
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I`ve never primed a mechanical pump, sometimes it takes a little while to get fuel to flow. If you crank it over for more than a minute and your not getting fuel, then you can suspect either the pump is bad, there`s a hole in the line somewhere, or a fitting has a bad enough leak to suck in air. If the pump is new, it`s a real good idea to pack the spring area with a moly lube, since chevy`s design doesn`t feed oil directly into this area, it needs the lube when it`s new in order to break in just like any new mechanical device would, if it goes without lube usually the spring overheats and will fail early or cause the diaphram to fail. One thing you can do to test the pump is to plumb it into a 5 gallon container of gas, then crank the engine over, since it`s a shorter distance and you know there are no leaks, it`ll tell you if the pump is bad. This would also help to prime it somewhat.
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Old 05-27-2005, 11:35 AM
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Same basic question, but a Ford mech. pump. This is a new installation so it's dry from the tank to the carb. Can you start a siphon AFTER the pump (perhaps where the fuel line enters the carb) or will the pump itself prevent that? Any other suggestions how to get the fuel flowing?
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Old 05-27-2005, 11:43 AM
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mechanical fuel pumps work on vacuum, they do not need primed. Blow back thru the hose. Is it clogged? does it bubble in the tank? does the air leak somewhere with no bubbles?
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Old 05-27-2005, 11:47 AM
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What engine are you working with cboy?If the fuel pump ecentric is loose or missing from the cam/timing chain it will not actuate the pump.Learned that lesson the hard way several years ago.Teenager who knew it all,dad laughed while I screamed and cussed.Then after an hour he set me straight.
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Old 05-27-2005, 12:02 PM
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Quote:
Originally Posted by RCastle
What engine are you working with cboy?
Your dad sounds like my dad. Always let me wallow in my own stupidity for a while. But it sure seemed to make each "lesson" a little more memorable.

This is a 460 Ford. Actually, I'm not having a problem (like Caprice), I'm just anticipating how best to "get ready" for the initial start up of the engine in a few days. If the vacuum created by cranking the engine over a few times will be enough to get gas through a totally "dry" system then I'll just go ahead that way. But if there are any "tricks" for getting the gas to the carb in a hurry...I'm all ears.

Dewey
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Old 05-27-2005, 12:32 PM
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pull the inlet hose off the pump and stick it in a fuel jug. Then take your airblower and stick it in the fuel neck going into the tank, use a shop towel to seal it somewhat. a couple of "poofs" should get some gas flowing.
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Old 05-27-2005, 01:03 PM
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prime

The best way to do it is to fill the carb by the vent tube. Get a small enough funnel or i use a squeeze bottle and fill the bowl of the carb up. The engine will fire instantly. With the engine running the fuel pump will fill instantly.........

Hands down the best way to get the job done....

A word of caution... if this is a new engine with a flat tappet cam you "DO- NOT" want to be cranking on it to get fuel into the carb!!!!!!!

bad things man, bad things!!!!!

Keith
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Old 05-27-2005, 05:27 PM
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Sounds like the easiest method, K-star.
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