'71 Dart starved for fuel

My '71 Dart Custom is starved for fuel before it reaches the carb. 318 V8 engine. I have replace the fuel pump, removed the disintegrated “sock” from the tank, and even moved the fuel filter higher up in the compartment to keep it away from the block and avoid vapor-locking. Even so, the fuel filter never gets more than one-third full, and when I hit the gas, the carb sucks the filter dry before the pump can catch up. I’m not talking about revving the engine to high RPM, just starting out from a dead stop or accelerating from 30 to 40mph. I’d say it stalls about 20% of the time from a stop. It has not yet stalled while accelerating at speed.

Once the engine is hot, the problem gets worse. The V8 surges and falls back as gas comes and goes…even at 25-30mph. It’s like driving a rocking chair…well, not that extreme, but you get my drift.

Does anyone have an idea what else I can do? I honestly don’t think it’s the carb, and I know the fuel flow is a little better since I replace the pump and moved the filter. Before that, there was practically no gas in the filter at all.

I have two ideas:

  1. there may be a hole in the fuel line someplace between the tank and the fuel pump. The fuel may not be leaking, but the pump will be sucking air instead of gasoline.

  2. the camshaft lobe that works the fuel pump arm may be worn so that the fuel pump doesn’t have a stroke as long as it should. The easy way out would be to install an electric fuel pump and fashion a block-off plate where the mechanical fuel pump is attached.

Remove the fuel line from the carborater and measure the fuel pump output, you should see at least a pint in 30 seconds.

Unless you’ve replaced the fuel tank you likely have rust on the inside of the fuel tank, mostly on the top of the tank from 40 years of condinsation. Without an inlet screen or sock inside the fuel tank you won’t go far. Install a new “sock”.

Use compressed air to blow out the fuel lines. Remove the new fuel pump and look inside the inlet nipple. There is a screen inside to stop debris from entering the pump. If it’s plugged with rust throw the pump in the trash. When you install the new pump install an additional filter before the pump or it will plug up again. Or you could replace the tank, they have become inexpensive for older cars like this one.

The carburetor cannot suck fuel from the filter. If the filter is filling with air that air is being forced in by the pump. @Triedag may be on target. A porous fuel line may be allowing the pump to draw air in. And those Mopar fuel pump wobbles would occasionally loosen and move toward center so that they would barely move the pump arm but first check the short rubber hose that feeds the pump. Before removing the tank to check the hose there you might sit a SAFE fuel can near the car and run a 3/8" rubber line from the pump inlet to the fuel tank to see if the engine will rev and keep the filter filled.

Lots of good advise so far…Do that flow test…I bet the pump is sucking air from a leak in the fuel line…Also, todays gasoline has much higher vapor pressure (which fuel injected cars can tolerate) This will cause vapor-locking on hot days in the old carbureted vehicles…

Thanks to everyone who responded so quickly. I will begin the testing and report the results.

Again, many thanks.

I assumed you replaced all of the rubber hoses. As to the condition of the fuel lines is there any sign of rust under the vehicle? Usually with leaky fuel lines that draw air you get a few drips after you turn the car off, it stinks.