I come from the pit bike world. All we have are filters that mount to the carb. We call them pod filters. Do not use k&n style filters in dirt riding k&n are for sand only they pass top soil and silt they work good for sand. Foam filters will pass sand and are good for top soil so pick wisely. The larger filter the better the less velocity through the filters the better they filter.
The pod filters are open to the elements and will suck water if a puddle is hit to hard. Keep that in mind.
Trikes:
1985 ATC 70 mod to 184cc
1984 ATC70 mod to 124cc
1983 ATC 70 Xmas restoration
Quads:
1986 TRX 250R
2002 TRX 400EX
2- LT80 for the kids
1986 LT 50