I believe the stock paper air filters are very good at filtering, they have a lot of area, and the filter traps most stuff.  It is a bit restrictive - but not out of character with the abilities of the CV carb or the restrictive exhaust.  If you change stock filter to a pod and don't do any other improvements.....you aren't going to notice much change in performance....although the sucking sound from the intake may fool you into thinking the bike is faster.   Most of the POD filters are not intended for a 650cc engine to be pulling through a single carb., and most POD changes are done for looks or to save weght when the stock air box is removed.

If you decide to make performance improvements.....then maybe even a POD is too restrictive.  They really don't have much filtering area.  My bike has a 4" diameter x 6" long foam filter to support the Stage 1 cam, VM36 carb, and less restrictive exhaust.

I'm running a stock filter with the trumpet muffler and a 150(?) main jet in my '86.Has more power than the '87 with an '02 engine and '87 carb set up with a cone filter and trumpet muffler.