Yes I saw that dirt in the "clean side" of the air cleaner, indictiave the sponge did not have a good seal 360 degrees OR the plastic cover , which does not have a gasket, allowed some dirt to get inside it on the "clean side".
My short term countermeasure is ensure sealing on the plastic cover & Sponge, I can DIY a thin gasket from Home Depot stuff.
Alright, I'm drinking some kool-aid here and willing to allocate $50-ish for intake enhancements.
http://gokartsusa.com/GY6-150-Engine-Air-Filters.aspx
How to spend it?