Those pleated element filters cause excessive turbulance in the airflow through the carbs disrupting the vacuum signal for the slides, this causes an off idle flat spot and steady cruising speed flutter. The shorter and more tapered the more the effect.
You can spend weeks trying to tune these out or put on a round foam filters. about 4 inches long are about right. I use Uni Filters. I like the two layer units. The coarser out layer traps big stuff while the finer inner layer gets the little stuff.
Leo