Fuel problem

Tiny
STALKER
  • MEMBER
  • 1978 CHEVROLET TRUCK
  • 5.7L
  • V8
  • 60,000 MILES
I put new tanks, new soft line, new hard line, new manual fuel pump and new carburetor. It will not stay running with the manual pump, fuel runs out after a few minutes of driving. Put a Holly blue and pressure regulator and it ran great for four months and the Holly has quit. Why will this truck not run on its manual pump?
Thursday, March 2nd, 2017 AT 4:47 PM

17 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 34,332 POSTS
It sounds like you are describing that it will restart after sitting a while, then repeat the starving for fuel. If that is correct, the most likely cause is a collapsing pick-up screen in the tank. They will stretch back out after sitting a few minutes, and will let gas pass for a few miles. That is worse when the highest volume of fuel must be pumped. That is during acceleration and highway speeds with a carbureted engine. That is during coasting with fuel injected engines that have the pressure regulator on the fuel rail on the engine.
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+1
Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
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Yes, that is how it is running, but the pickup tubes are new as well.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
CARADIODOC
  • MECHANIC
  • 34,332 POSTS
The sock is on the end of the pick-up assembly, and can be slid off easily. Was the old sock reused or replaced with a new one?
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
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  • 9 POSTS
It was replaced with a new one. It has two tanks, runs the same off of both. I have even ran from one tank bypassing the tank selector thinking it might have been bad or sucking air from it.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,241 POSTS
If you pull the fuel line off the pump and crank the engine over do you get a good supply of gas?
If you remove the pump and rotate the engine slowly does the pump push rod move about 1/2". I have seen pump drive lobes wiped off cams a couple times.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
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Yes, it gets good fuel when spun over. As far as cam lobe, it has less than 60,000 miles on new crate engine.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,241 POSTS
I've seen lobes go in 1/2 hour of running, they were not heat treated correctly.
How much fuel pressure do you get out of the pump? I would still pull the pump and check the push rod and the pump arm. Have seen the arms break free.

Other than that what filter(s) do you have? You don't still have the pressure regulator inline do you?
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
STALKER
  • MEMBER
  • 9 POSTS
Pushing around 7 psi on fuel pressure. It will drive about 6 miles before acting up. It will set and idle all day. Regular was removed when the Holly went down.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,241 POSTS
Stock carb? Air cleaner? When it shuts down, if you pull the air cleaner and move the throttle do you see fuel from the squirters? 6 miles easy throttle?
Have you checked the float just to be sure it doesn't hang up under throttle?

Very strange issue.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
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Very strange indeed, new Edelbrock 650. When it shuts down, no, there is no fuel, after 10, 20 minutes it will start right up and go again, about another 6 miles. Less if I get on it. Like I said before, it ran fine on the Holly Blue but something not right, it should not have burnt up in 4 months. It's down this from day one, it's the reason I put the Holly on it in the first place. Can't get it to stay running on manual fuel pump. Everything is new from tanks to carburetor. Engine, trany and rear end are all new as well. Very confused here, I've done all I know to do to it. Gonna pull the bed and remove the screens off the pickup tubes today, see what that does and go from there.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,241 POSTS
Sounds like you did a custom build, replaced all the pieces and had this problem on initial start correct?
When the electric pump was installed was it up front and drawing through the fuel system, or in the rear pushing fuel?
I'm going to guess it was up front, basically bypassing the manual pump and drawing through the flex line connected to the hard line on the frame?

If that is the case, remove that rubber line and the line from the selector, Blow air through it from the pump end to the selector and see if the line is clear, then try the other direction. I'm thinking you have either a bad rubber line (collapsing or internal damage like the way a brake line can fail and become a one way valve) or there is something traveling the hard line.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
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I want to thank you guys for your help and new insight. It turns out it was the screens on the pickup tubes. I removed them and added a couple filters and it's running great. Thanks again.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,241 POSTS
Glad you got it sorted. Must have been a bad batch if they were blocking the fuel that bad. Do you recall the brand?
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
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  • 9 POSTS
I believe is was an AutoZone brand. Duralast I believe.
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
Glad you could get it fixed please use 2CarPros. Com anytime we are here to help

Nice Guys!

Best, Ken
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,241 POSTS
CARADIODOC who suggested the fuel socks :)
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Tuesday, August 13th, 2019 AT 9:25 AM
Tiny
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Thanks again, I will use this again and pass it along to my friends.
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Tuesday, August 13th, 2019 AT 9:25 AM

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