Air Filters for Off-Road Dirt Bikes and ATV's - K&N Replacement Air Filters are ideal for extended use in dirty and dusty off-road riding and provide clean carburetion even at high altitudes. As a rule, no jet changes are required with just a K&N air filter element... the spark plug condition should be checked for proper mixture after the first few miles of riding. If the airbox has been modified for increased air flow, the main jet size will need to be increased to provide the proper fuel mixture.