Air filters supplied with the Termi kit
I checked mine after approximately 500 miles of running and could not beleive how much crap there was in the ends and up the sides, it looked like approximately 50% of the filters surface area was totally blocked. I swear I have not been grass tracking or competing in any enduro's!
It may be worth a look if performance feels like it is dropping off. The filters are easy to get at with a 1/4 drive extension and wobbly end.
I used an air line, a bit of brake cleaner and some Pipercross filter oil to re-oil them.