Two things come to mind, one is fuel pump pressure. The other is this, I have been running an Ebrock carb since 88. I have had to fix/replace leaky floats three times since then. Since you say the Carters did the same it may not be it, but they use the same style floats too.

I would start with the fuel pump pressure and maybe double check the float settings.

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They say there is always the exception that proves the rule.
Don't be the exception.