There are many, many things that can cause plug fouling, besides the carb.

First, are you sure it's gas fouled and not "burning oil?"

What do the plugs look like? Describe the color, or can you post a picture?

Are all 8 plugs the same? Or are just a few, or one or two fouled?

You might have gotten the wrong plug heat range.

Does the engine idle and run smooth, or does it idle ragged, same with low speed cruise?

Is the car running up to temperature? That is, do you have a thermostat, and is it allowing the engine to come "up to" temp?

It might be a problem in the EGR system, or you might have a PCV valve stuck open

IF it is the carb, it is probably not the idle circuit per se. It might be a leak in the carb--I hated Carter "Thermojunk"

In the case of the older Holley's I've found MANY leaking power valves--brand new right out of the "rebuild kit."

Carters don't use that type of valve, but the metering rods might be stuck with the needles pulled clear out of the jets, allowing a rich condition.

It's been a long time since I've had a Carter--and you need to find out, is it an AFB, an AVS, or a Thermoquad--it IS a 4bbl? or is it a 2 bbl?

Anyhow, most of the Carters used a vacuum operated piston with a spring underneath. The high vacuum pulls the piston down, and pulls the needles (which are tapered or stepped) down into the jets, to lean the carb out for idle and light cruise. As you apply throttle, the vacuum drops, the spring pushes up the piston, the needles start to come out of the jets, and they effectively get larger for more power.

There are many questions here, before you condemn the carb

 

If fuel is spilling over the top, you most likely have a float/ needle and seat problem, rather than metering rods.

If this has a foam float, they can become waterlogged, and of course brass floats can leak.

You might have a poor needle and seat, one that is letting fuel seep through.

Also, are you running any kind of "performance" fuel pump? Any chance you have too much fuel pressure?

 

Yes, could be too much pressure. You should be able to buy (still yet) those combo vacuum/pressure gauges at the auto parts, and they are occasionally handy to have around. Look up the pump you bought and see what it should have for pressure.

Frankly, though, I doubt the pump is the problem. There is only one way to be sure--check the pressure

Again, I've said this before--as old as these cars are getting to be, suspect almost ANYTHING

 

My old books of course shows higher pressures for the higher performance engines.

For HP 440's it shoes up to 7 1/2, and hemis shows up to 8 1/2. I'd forgotten that any were that high.

I'd say that if you have an old needle and seat, that anything above about 6 is suspect. Certainly anything above the hemi spec is not good.

Here's the thing about mechanical pumps. The pressure is not generated by the cam lobe, it is generated by the spring in the pump. When the cam actuates the pump lever, nothing happens. The SPRING in the pump does the work, and so this means three things:

It is the spring in the pump that determines pressure

When the line builds up, as at idle, the lever starts to "float" of the cam lobe because of fuel pressure, and thus doesn't do as much work

If you run an electric pump in series, the electric doesn't add much pressure, because all that happens is, that the mechanical pump arm starts to float, and adds nothing unless it's needed.

As I've said before, as old as these cars are, suspect anything. Take a critical look at the floats and needle and seats.