74 Duster 318 Fuel Supply issue? Only draws at full tank!

[Gooner04]

Hi! I’m wondering if anyone can shed some light on this issue. I’ve searched around on FABO and could not quite find a similar question, so here goes.

I’m helping a friend diagnose his fuel issue on a 74 gold duster with a 318. He had an aftermarket Fuel Sending Unit put in, and since then the car will not draw fuel once the tank gets below 3/4 full. It just acts as if it ran out of fuel.

The engine has an Edelbrock 4bbl carb that replaced the original 2bbl. This issue did not exist after the carb was first installed. They also put in a new fuel pump at the time they put the carb in. Not sure about the lines or tank.

From what I can tell, his guage does read the tank level accurately. He thinks it’s a sending unit issue. I wonder if it might be a pump or fuel line issue because the guage seems to work but fuel delivery gets poor after the tank goes down even a little bit. Has anyone experienced this kind of issue?

 

[Dana67Dart]

So are you saying that when the tank get to (fuel gauge display) 3/4 tank that the car is starved for fuel?
Does the engine quit and you have to add fuel to the tank to restart?
Does this happen hot and cold?

Fuel pickup could be installed at an angle, so at 3/4 tank the pickup is out of the fuel????

Will the guage read below 3/4?

How did you get it there if engine won't run past 3/4 tank?

 

[diymirage]

sounds like a improperly clocked pickup (as mentioned)

or...a hole on the pickup

 

[cudamark]

Does the engine run properly with a full tank? Say, full throttle in a low gear going up a steep hill? The only other thing I can think of is a weak fuel pump that is helped by a higher fuel level that acts a bit as a gravity feed to the pump.

 

[AJ/FormS]

Check the clamps on the rear jumper.
If gear clamps, there should be 2 on each side staggered 180* and make sure the jumper is not kinked nor sucked flat. The hard-lines should be properly flared on both sides. Make sure the tank is vented