New to me engine, never lake tested. I've cleaned the carbs and changed the fuel filter, new plugs, fresh fuel.

When idling in a barrel the rpms are low about 575-600 unless I advance timing a few degrees from 5° atdc. Mixture screws set at 5/8 turn.

My old omc 60° v-4 would idle with butterflies fully closed, but I see an adjustment on these carbs. Can I raise idle speed by opening the butterflies or should I look elsewhere?