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Old 07-17-2019, 02:41 PM   #1
Anthony14
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Fuel pump

Hi guys. I have a SBC350 with a TH350. TCI 2500 Stall, 3.42 gears, Brodix IK200 heads, 224/234 cam with .491/.519 lift. Holley 750VS, Edelbrock Performer RPM intake.

Took my truck out for a cruise and hammered the gas. Pulled through 6500rpm, I shifted into second, then when crossing 5000rpm it started bucking and kicking like it was starving for fuel. I did this 3 times and everytime was the same. I'd let off the gas, she'd catch up, and continue to cruise normally.

I feel like if this was a ignition problem then regardless of what gear I'm in it could happen constantly at that rpm. I'm thinking my mechanical fuel pump is going; I'm burning up the fuel in the carb through the initial first gear pull then by the time I hit second the carb is empty and the pump can't keep up.

This is the second NAPA fuel pump, first one just flat out died. I pulled up the specs and it's only rated for 23GPH. After doing some research I'm not sure that's even close to sufficient. I have 3/8" fuel line front to back. I'm thinking I need a fuel pump and considering the Edelbrock 1721.
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Old 07-17-2019, 04:19 PM   #2
Steeveedee
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Re: Fuel pump

Maybe pull the sock on the sender in the tank and see if it is clogged some. It doesn't take much when it's working on suction instead of pressure when it comes to fuel flow. Do you have a filter between the tank and the pump? If so, that would be a place to look, too. Squeeze you fuel line between the tank and the pump to make sure it isn't too soft and collapsing.
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Old 07-17-2019, 04:28 PM   #3
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Re: Fuel pump

Might be the float settings, did you check them?
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Old 07-17-2019, 04:33 PM   #4
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Re: Fuel pump

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Originally Posted by Steeveedee View Post
Maybe pull the sock on the sender in the tank and see if it is clogged some. It doesn't take much when it's working on suction instead of pressure when it comes to fuel flow. Do you have a filter between the tank and the pump? If so, that would be a place to look, too. Squeeze you fuel line between the tank and the pump to make sure it isn't too soft and collapsing.
I should have mentioned; tank is brand new, Camaro tank that's at the back of the truck. Sending unit is brand new as well. All rubber is new, and any joins are under 2" of rubber in length. I do have a filter after the pump before the carb and it's clean.
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Old 07-17-2019, 04:34 PM   #5
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Re: Fuel pump

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Might be the float settings, did you check them?
Still just below the sight windows, rock the truck slightly and fuel spills out.
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Old 07-17-2019, 04:44 PM   #6
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Re: Fuel pump

What kind of ignition, HEI or points? And what is the initial timing? And 23GPH is way low, should be 80+ GPH...
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Last edited by Ironangel; 07-17-2019 at 04:50 PM.
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Old 07-17-2019, 04:59 PM   #7
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Re: Fuel pump

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What kind of ignition, HEI or points? And what is the initial timing? And 23GPH is way low, should be 80+ GPH...
It's a Taylor HEI 640000 distributor. MSD Streetfire wires, with the plugboot protectors. I can't remember exactly, I want to say initial is around 10, and all in is 36.

I figured 23GPH is too low. I found a formula online and if my combo puts out about mid 400hp I should be at around 40GPH at a min, so makes sense to just flat out upgrade.
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Old 07-17-2019, 05:14 PM   #8
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Re: Fuel pump

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Originally Posted by Anthony14 View Post
I feel like if this was a ignition problem then regardless of what gear I'm in it could happen constantly at that rpm. I'm thinking my mechanical fuel pump is going; I'm burning up the fuel in the carb through the initial first gear pull then by the time I hit second the carb is empty and the pump can't keep up.
So may I ask. Does your RPM drop under load? Does the same amount of foot feed result in the same RPM under varying load? Maybe it's not the RPM explicitly. Just an interpretation of the response.

Perhaps it's your throttle linkage. Check out my post here. You never know what evil lurks in that linkage. Assume nothing.

http://67-72chevytrucks.com/vboard/s...d.php?t=742187



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Old 07-17-2019, 05:29 PM   #9
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Re: Fuel pump

I agree it's your fuel pump. Looks like Summit Racing has a Edelbrock clone for about 1/2 the price. Might want to check it out.

https://www.summitracing.com/parts/s...20-1?rrec=true
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Old 07-17-2019, 05:47 PM   #10
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Re: Fuel pump

Quote:
Originally Posted by jeffahart View Post
So may I ask. Does your RPM drop under load? Does the same amount of foot feed result in the same RPM under varying load? Maybe it's not the RPM explicitly. Just an interpretation of the response.

Perhaps it's your throttle linkage. Check out my post here. You never know what evil lurks in that linkage. Assume nothing.

http://67-72chevytrucks.com/vboard/s...d.php?t=742187



j
If I'm understanding your question right; yes, the rpm drops when going up hill without adjusting my foot position. I would have to give it more gas to maintain a constant speed.
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Old 07-17-2019, 05:49 PM   #11
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Re: Fuel pump

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Originally Posted by tdangle View Post
I agree it's your fuel pump. Looks like Summit Racing has a Edelbrock clone for about 1/2 the price. Might want to check it out.

https://www.summitracing.com/parts/s...20-1?rrec=true
I'll check it out. Thanks.

Editied: I ended up ordering and ACDelco unit part #12355612 from RockAuto. Should be more then enough at 110gph, and with the 3/8 fittings everything should fit.

Last edited by Anthony14; 07-17-2019 at 06:31 PM.
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Old 07-17-2019, 07:37 PM   #12
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Re: Fuel pump

One more thing- is the fuel pickup at the rear of the tank? Maybe the fuel sloshes back and you don't have the pickup submerged in fuel?
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Old 07-17-2019, 08:31 PM   #13
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Re: Fuel pump

Check your fuel filter(s). Even if they are fairly new it doesn't take long to clog if you are running the origiial tank. I have to change mine about once a year.
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Old 07-17-2019, 10:36 PM   #14
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Re: Fuel pump

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Originally Posted by Steeveedee View Post
One more thing- is the fuel pickup at the rear of the tank? Maybe the fuel sloshes back and you don't have the pickup submerged in fuel?
Pickup is middle of the tank, and the tank was over half full.
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Old 07-18-2019, 04:58 PM   #15
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Re: Fuel pump

"Bucking & kicking" sounds like maybe the hydraulic lifters are pumping up. 6500 rpm is pretty high for hydraulic lifters.
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Old 07-18-2019, 05:52 PM   #16
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Re: Fuel pump

Quote:
Originally Posted by Anthony14 View Post
It's a Taylor HEI 640000 distributor. MSD Streetfire wires, with the plugboot protectors. I can't remember exactly, I want to say initial is around 10, and all in is 36.
Do the instructions say how much mechanical and vacuum advance it provides? Is the vacuum advance adjustable?
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Old 07-21-2019, 09:28 AM   #17
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Re: Fuel pump

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Do the instructions say how much mechanical and vacuum advance it provides? Is the vacuum advance adjustable?
I tried searching it can't seem to find any specs. It is adjustable.
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Old 07-21-2019, 02:20 PM   #18
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Re: Fuel pump

Before buying any parts I would determine where the problem was. You could hook a temporary fuel guage up and determine for sure if fuel supply is the problem.
I had very similar problem years ago on my GTO caused by running an air cleaner base plate without the top. Not that that is your problem but I went through the whole ignition system (swapped distributors, bypassed the resistance wire etc) and the fuel system (changed fuel pumps, tore the q-jet apart at least twice, and dropped the fuel tank to inspect it.). Before I sat down and started testing things logically I was just wasting time and money.
Good luck.
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Old 07-23-2019, 10:05 AM   #19
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Re: Fuel pump

So took the fuel pump out, came out in pieces. I'm surprised it even ran. Looks like the swaged in axle for the pump lever broke the swag in the pump.
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Old 07-23-2019, 10:13 AM   #20
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Re: Fuel pump

See pic.
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Old 07-23-2019, 10:24 AM   #21
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Re: Fuel pump

Wow, shocked you could even get it to move. Glad you figured it out You mentioned possibly going with the Edelbrock 1721 pump. I recommend it, never any problems with mine. A little pricey, but well worth it. They do not have a return line tho.
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Old 07-23-2019, 02:20 PM   #22
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Re: Fuel pump

I went with a ACDelco 12355612 110gph pump. What a difference in design. The lever axle has it's own boss so the failure I experienced would be impossible. The lever itself is a riveted together 3 piece design instead of a stamped piece. Took it out for a drive and drives normal again.
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Old 07-23-2019, 08:52 PM   #23
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Re: Fuel pump

Quote:
Originally Posted by Wrenchbender Ret View Post
"Bucking & kicking" sounds like maybe the hydraulic lifters are pumping up. 6500 rpm is pretty high for hydraulic lifters.
George
Shifting into second at 6,500 is out of the "powerband" most likely as well. Shifting closer to 5,500 RPM would be better.

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So took the fuel pump out, came out in pieces. I'm surprised it even ran. Looks like the swaged in axle for the pump lever broke the swag in the pump.
Ouch... that looked fun... glad you found it right at the get go.

Gary
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Old 07-24-2019, 04:02 AM   #24
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Re: Fuel pump

Quote:
Originally Posted by Anthony14 View Post
I went with a ACDelco 12355612 110gph pump. What a difference in design. The lever axle has it's own boss so the failure I experienced would be impossible. The lever itself is a riveted together 3 piece design instead of a stamped piece. Took it out for a drive and drives normal again.
Cool Beans! That new pump will also allow you to clock the lower housing to maximize flow and minimize bends in the fuel lines...Well done!
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