Bear in mind the sand and lil bits of gravel that would love to check out the inside of your cylinder o.o
These "air filters" may not be the best in the world but they at least try to help keep the bigger chunks out. As they are really only a "filter" in the loosest sense of the word - removing them wouldn't really do anything to improve flow noticeably unless they were so gummed up with filth they actually managed to restrict.
In which case you should not only just clean the thing, it's evidence of how some sort of filter is actually needful.
Even if you don't play on trails - roads themselves are obviously covered in sand and grit. The rear tire is positioned perfectly for throwing all sortsa crap right at the intake, which is happily drawing in as much as it can. Even with the stock filter & cover in place I would have water in my float bowl after a ride on wet roads - let alone in the rain.
Given I can hold up the stock filter sponge and actually see through the holes easily enough to read this post (yar - I just tried it lol) I daresay that any perceived "performance gain" from removing it entirely would unfortunately be either coincidence and/or a placebo effect. When I constructed my remote airbox with a real sponge filter I was very concerned with potential performance loss and inadvertently enriching the mix - so I paid very close attention to before and after via GPS and plug coloration.
There was NO perceivable change (other than it being significantly quieter lol).
The stock cover itself (the black plastic one, not the louvered chrome one) may be a touch restrictive - that's easy enough to fix by making the three tubes into one hole with a drill/dremel/whatever.
In all seriousness - I wouldn't run without a filter, it's just begging for trouble. Even if there was a performance gain you'd loose it quickly enough as your piston rings, cylinder, and piston itself were ground down to chipped, scoured nothingness. ONE tiny bit of quartz gravel will happily kill your compression.
