[440roadrunner]

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