Idling too high for one thing, and possibly the filter top is too close to the top of the carb. Idle mixture would be rich from the throttle plate position you now have.
Lower idle to 675 to 725 or so, then reset the mixture screws. They want to be close to 1-1/4 to 1-1/2 turns, any different setting and the idle circuit is being adversely affected by throttle position at idle or the idle fuel oriface sizing.
High flow air filter element shouldn't have an influence on idle speed or quality. Off idle, mid-range, top end would be affected.