Thanks for the reply Jason. Looking into this it is pretty clear that you and Remo are right and for maximum filtration the filter, be it foam or otherwise ,should be oiled.
The fact that Iame do not include oiling the filter in their maintenance schedule suggests to me that they do not expect users in general to be doing so and failure to do so will not be catastrophic.
The filter may be preoiled at manufacture but even a dry unoiled filter must be pretty good compared with no filter. The inner foam section looks as if it should be fairly effective.
Historically front runners in UK and elsewhere were running 100cc 20k rotary valve engines (tillotson on side of crankcase next to back tyre) with nothing over the inlet.
Doubt if Senna ever had any sort of filter on his engines. Seems crazy.!
The 'torpedo ’ style air boxes were introduced later but only to quieten the karts, still no air filter.
To my knowledge the first manufacturer to fit an actual filter was TKM with their BT 82 piston port Yamaha KT beater in the US market. ( Dry foam no instruction to oil)