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Fuel systems Q&A Carbs, injection, tanks, lines, pumps, everything fuel system related!

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Old 03-01-2021, 07:10 AM
lazarat's Avatar
lazarat lazarat is offline
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Join Date: Feb 2018
Posts: 348
Default Fuel question

Have the 20 GPH electric pump close to tank. Old steel line connecting to rubber hose to pump, rubber line from pump to original frame mount steel line, then rubber hose to filter then carb.

On occasion, when running awhile, I hear the fuel pump going nuts, and the filter is bubbling like crazy. Yesterday when on the way back from a show on the interstate, I had the Holley 650 opened up, and after a few minutes of that, its starts to act like its running out of fuel and bucking. I slowed down in the right lane to give the pump time to catch up. (This has happened before)

When I got off the interstate i can hear the fuel pump "going nuts"...that is, louder and cavitating? Filter bubbling like crazy.

The rubber line from steel frame line runs up between water pump and engine (SBC) to carb, but not too close, has room. Questions:

Is it getting to hot?
Is the pump still too small? Had a 9 GPH when I got the car.
Should I install a new steel line to rubber from tank?
Is it an all of the above situation?

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Old 03-01-2021, 09:27 AM
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I-R-POPS I-R-POPS is offline
''Rusty Mopar Slacker''
Join Date: Aug 2012
Location: Tome, New Mexico
Posts: 4,002

I've had the same issues on several rides and here is my go to cure. This is what I do on every thing I build to avoid it.

I put in a new in tank fuel pump, a good inline filter, a pressure regulator with a pressure gauge and a fuel return line to the tank.

Make sure you're not running too much pressure to your carb especially if you're using an Edelbrock carb.

It works for me and my Mopar addiction.

Good luck.
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Old 03-01-2021, 09:55 AM
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Old Iron Old Iron is offline
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Join Date: May 2011
Location: Willard Mo.
Posts: 13,292

I'm with POPS
I just cut to the chase and replace all the lines, pump and filter with new stuff.
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Old 03-01-2021, 01:46 PM
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MercuryMac MercuryMac is offline
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Join Date: Jan 2013
Location: Northern Alberta, Canada.
Posts: 3,740

If the pump is going crazy, it's trying to keep the pressure up but can't. Maybe there's a little piece of something that catches under a valve in the pump and holds it slightly open. My guess though is that you have a cracked line in the intake side of the pump, probably right in the tank. Does the problem occur when you have a full tank of fuel or mostly when you are below half full? When the gas is covering the 'in tank' line crack, the pump will suck gas and everything is cool, but when the gas level falls below the crack then the pump starts to suck air.
Good luck.
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Old 03-01-2021, 05:43 PM
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Dr Crankenstein Dr Crankenstein is offline
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Join Date: Mar 2011
Location: SK CAN
Posts: 7,971

I also believe your pump is starving. What's your tank/pickup arrangement?

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Old 03-01-2021, 08:04 PM
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lazarat lazarat is offline
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Join Date: Feb 2018
Posts: 348

Cracked line, starving for fuel.

Hiding in plain sight, what looked like a good hose on the suction side turned out to have a crack on the top that was unseen. Plus, this hose was also a bit oversized.

This problem i was having also did occur when the fuel was low in the tank. The outlet is a bit above the bottom of the tank, as it has the sweep inside where the sock filter should be. Also the bends in the outlet line curved a bit upward, I brought all in line so there was a better flow, replaced the short hose to pump with a better fit and have the steel line up against the pump secured by said hose.

We shall see, going to make sure fuel doesnt get too low, I am sure it will be fine and thanx for responses.
Its always something.
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Old 03-03-2021, 10:45 AM
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sneakysnake sneakysnake is offline
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Join Date: Dec 2009
Location: Oklahoma
Posts: 2,697

My thoughts are check the line between pump and tank. Like said above sounds like having a cracked straw, sucking in air some where. Hopefully it's not in the pickup tube in tank.
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