383 2 bbl carb question

[la.68charger]

just getting back in Chargers after 15 yr. absence. Just bought '68 charger with stock 383 2bbl. The carter 2 bbl doesn't have mixture adj. screws, the place where they should be is sealed with a metal cap. I assume the carb has no easy way to adjust idle mix. Car is idling rough, but smooths out above idle, suggestions? I do have the original carb, which has mix adj screws, but it needs rebuild.