Simple fuel line question

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Sep 30, 2017 | 09:46 PM

columbia1spring

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Simple fuel line question

This is an easy question, i tried to find the answer threw searching but to no avail...
74 390 2bbl from the factory...
it now has a 4 bbl manifold with an adaptor plate converting it back to a 2100 2bbl. Yes! thats not a typo.
My question is, the fuel line from the stock fuel pump to the carb, I know whats on there now, but, what should it be? 5/16 or 3/8?

Sep 30, 2017 | 10:07 PM

DB429SCJ

Laughing Gas

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From: Buffalo NY

OEM line is 5/16.

Sep 30, 2017 | 11:49 PM

PapaBearYuma

Cargo Master

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From: Great American SouthWest

^^ x2 on that.

Tank to fuel pump is 3/8", fuel pump to carb is 5/16". I think the pressure and velocity increase are to prevent vaporlock.

Nov 24, 2017 | 08:39 AM

Rufus1945

Freshman User

Joined: May 2016

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From: Central AZ

Yes, but how do you connect the two together when deleting the fuel pump. I installed an electric pump at the tank and can't get fuel to the Holley carb

Nov 24, 2017 | 09:55 AM

Jklnhyd

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Joined: Sep 2013

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From: Pasadena, Ca

You asked how to get fuel from the stock pump to the stock 2100. And now you ask how to get fuel from an electric pump at the tank to a Holley?

Nov 24, 2017 | 10:30 AM

Idaho Highboy

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From: North Idaho

Rufus, you should be able to find a double-male adapter to convert 3/8" to 5/16" at any hardware store - assuming you aren't trying to run everything with hard line.

EDIT: Jake's comment below sparked a memory. You could also just buy a threaded adapter that converts, and bolt it into your carb's fuel port. Agree that I'd keep things past the pump at 5/16", but that's just the old guy in me talking.

Nov 24, 2017 | 11:25 AM

JakeHan

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Joined: Jun 2005

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^ like above, an adapter barb, possibly have to do it in 3 pieces, 3/8" to MP, coupler, MP to 5/16", but see what you can get for brass and use your imagination

. If you're jumping to the factory hardline, you can probably squeeze a 3/8" hose down to 5/16" with a worm clamp, or better yet, squeeze the 3/8" line onto a 5/16" inline filter (I know it'll grab on a barb filter fitting), then 5/16" out to the carb.

I'm pretty sure you can get a 3/8" fitting for your carb, too, depends on which one you've got. I prefer smaller lines on the pressure side, like was said, I've been told it's better for vapor-lock resistance.