Carter/Eddie AFB question

Try some bypass air. You can get it from the air cleaner to the carb and adjust the flow rate with a restriction or PCR valve. The idle channel restrictor maybe too small to let enough air through the idle circuit to sustain a high enough idle.

The 1406 has a lean calibration so you may need to open up the IFR. You can also drill and tap the primary cluster for adjustable holley air bleeds.