air filter service! it's called "doin' the nasty" in the dirt bike world!
dont hate me boys (too late i know) but....twin-air fan here!
clean up: swab out the air box and chassis rails first, then, i clean in gas, water, soap-n-water, done.
oiling: i have a lil tupperwear bowl with my air filter goodies in it. put about two inches of oil in the bowl, dunk-n-roll, GENTLY pursuade the oil all round over a small funnel letting the excess drain back in the can. set the filter aside, let the carrier evaporate a couple hours while i do other stuff then gently pat with a towel inside and out to get off excess if any. grease the rim in the air box a smidge then install.
regardless of what you use-
be gentle.
leaning an air filter can/will degrade it. twisting and wringing it will kill it NOW. gently fold or knead the filter to get the oil to and fro. same with cleaning, be gentle and support it if its water-logged, dont whip it by the rim to get water off. watch it with extreme water temps hi or low as itll kill the glue. before oiling after cleaning inspect the glued seams for splits. esp a factor for 4-strokes. they need pure clean air to live. i dont recomend washing them in a machine for obvious reasons.
treat them like a very fine garment, do it by hand. i replace mine after 5-6 cleanings at the very most. if i go dune hopping in poof-sand i toss it when i get home. cheap insurance. check your filter frame for flashing and burrs and round off as required.
look in the boot for debris. some stuff falls in when you yank the filter. check the box to boot seals too!
on a 4-stroke ALWAYS use a flame arrestor! dont try and convice me otherwise!
never plug the drain hole in your air box to keep spooge from dripping out. let it drip, if it pools it's a fire hazard.