Holley carb experts? Others? Why is my truck's fuel bowl being sucked dry? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-22-2003, 09:58 AM
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Post Holley carb experts? Others? Why is my truck's fuel bowl being sucked dry?

I'm at a total loss.

First I should introduce my truck. Oh yeah, and I'm new here too. I have a 1988 chevy pickup. It's a regular cab, shortwheel base model. The TBI 4.3L is gone, and I have a 330 deluxe GM crate engine in it (350ci, 330 hp). It turns a Th400 and that goes to 3.43 gears. I retained the EFI pump, and I run a return style Mallory AFPR to regulate down to ~7 psi for my carb. The carb is a 4160 600cfm Holley.

Well, Saturday my fuel pump dies and leaves me stranded on the side of the road. I replaced it the following Monday, and my beauty fired right up! Took it for a ride Monday night, and it was running out of fuel by 4000 rpm in low. It's like my fuel bowl was sucked dry. I increased my fuel pressure slightly and the fuel starvation problem slightly improved.

With the old pump, I never had problems getting enough fuel to the engine. So, I assume it's the AutoZone "Master" pump. I brought it back and changed it out this morning for an AC Delco pump. Sad part- it continues to do the same problem. I put my old fuel filter back on, and the problem continues. So, the pump should be good and the filter too.

Perplexed, I wet the tires, and had a friend powerbrake my truck (in the grass) while I watched my fuel pressure gauge. It didn't budge, but again the engine ran out of fuel.

Now, going down the road you can nail it and it's wonderful... like before the pump died. Then, it falls on it's face at the end of first and you have to remove your foot from the accelerator before it will even idle. So, I can run the bowl dry, and it'll die. Then let off the pedal, and it comes back to life, but you better not touch the pedal or it'll suck it down again. If I were to wait 5 seconds and try to cruise at whatever speed it would be, the truck will severly surge, like it's sucking the front bowl dry and then using whatever fuel enteres the bowl. If I coast for 10/15 seconds, the bowl will refill, and I'm good to go, but it'll do it again if I accelerate hard.

It will also run out of fuel moderately accelerating to try and merge on the interstate.

How could this be? My new pump is doing fine-I think. Nothing like this was happening before the OE pump died. I can't say my supply line is too small b/c it was just right with the old pump.

Any Holley experts out there? Help me out please.

Thanks,
Ben T.

[ May 22, 2003: Message edited by: MuscleTruck ]

[ May 22, 2003: Message edited by: MuscleTruck ]</p>

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Old 05-22-2003, 11:03 AM
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Although you've checked a lot of stuff,I still believe that it is a supply problem and not with the carb.Fuel pressure and flow volume don't neccesarily go together. Having said that ,you might check the bowls at the level hole and see if there is correct level, if not, maybe run an external little electric pump and see if it comes up. Back to supply, you mentioned filter, did you replace the sock in the tank? Did you check the pressure of the old pump prior to replacement? That may have been a by-product of the problem you have now. Prior to fuel delivery failure was the truck jacked up or bottomed where it may have kinked a line? It sounds like the problem may have been what caused the old pump to fail (or stop delivering fuel).
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Old 05-22-2003, 01:41 PM
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Whene the old pump went bad it may have blown part of the rubber diapham into the carb needles and seats. sounds like a restriction somewhere in the fuel line from pump to carb. Try raising the floats 1/4"
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Old 05-22-2003, 05:15 PM
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Setting the fuel level should be the first thing you do before attempting to make any further adjustments.The float level should put the fuel level just below the bottom of sight plug hole. You will make the adjustment with the vehicle on a level surface and the engine idling. You will first remove the sight plug, then to make your adjustment you will need to loosen the lock screw on the needle and seat. This will allow you to turn the adjusting nut to raise or lower the float level. Each hex flat on the nut will change the float level approximatly 1/32". Clockwise is less and counter-clockwaie is more. When you have the fuel level just below sight plug hole you will then tighten the lock screw and reinstall the sight hole plug. Make sure you have a shop towel handy in case you have any fuel leaks from the Sight plug or needle and seat adjusting nut.Let it idle a bit between adjustment's for it to stablize.
You can back the needle jet out with the hex nut with the motor SHUT OFF to check to see if there is something plugging it. When you put it back in have the jet 1/2 of the nut thickness down below the top of it and you will be close to the setting.

[ May 22, 2003: Message edited by: 1BAD80 ]</p>
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Old 05-22-2003, 08:37 PM
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I'm still learning about all of this guys.

It appears that when you buy a new fuel pump you have to readjust everything on your carb! I only checked a few of my carb parameters. They seemed "close enough". I didn't understand this.

Well, anyway I went to a friends house tonight, and we tuned up all of the settings on my carb. The idle mixture and float level got a lot of attention. I went up a few sizes on my squirter and we played with the fuel pressure.

It seems that the pump is working fine, and that my carb just needed adjusting to work along with the new pump.

I feel like an idiot for not having done more simple things first. I'm still learing...

Thanks for all of the comments guys. My truck's running as crisp as EFI right now. Let's just hope the weather doesn't change a lot.

Ben T.
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Old 05-23-2003, 12:36 AM
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i would try a high pro. mechanical fuel pump.
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