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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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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Might be the float settings, did you check them?
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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...
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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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Perhaps it's your throttle linkage. Check out my post here. You never know what evil lurks in that linkage. Assume nothing. :chevy: http://67-72chevytrucks.com/vboard/s...d.php?t=742187 j |
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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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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. |
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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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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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"Bucking & kicking" sounds like maybe the hydraulic lifters are pumping up. 6500 rpm is pretty high for hydraulic lifters.
George |
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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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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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:eek::eek::eek: Wow, shocked you could even get it to move. Glad you figured it out :metal: 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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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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Gary |
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