The idle circuit in the Carter BB-1 has TWO idle tubes, not just one. The one in the top casting is in plain sight. The one in the lower casting is hidden in the same passage that the the one from the top casting fits into.

Failure to remove the lower tube and clean the passageway beneath the tube will often result in the idle circuit being non-functional.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop