You should look at cleaning your air filter after every ride, after cleaning your bike check the air filter to see if needs cleaning. Generally if you can't see the original colour of your filter or even the writing on it then its dirty and needs replacing.
- Remove the filter from the bike, if the filter has inner and outer filters then separate them.
- Wash each filter in Air Filter cleaner or Kerosene. Do not use petrol, it will do a great job of cleaning but will also dissolve to glue holding the filter together.
- Squeeze or compress the filter to remove excess cleaner, do not try to wring it dry as this can tear the filter.
- Now wash the filter in warm soapy water, removing all additional dirt. Then rinse in warm clean water and squeeze it to remove all excess water.
- Inspect for tears or cracks, replace the elements if damaged otherwise hang the filter elements to dry.
- When dry re-oil each element. I have a bucket that contains air filter oil so I immerse the filter completely in the oil then squeeze as much excess oild out of the filter as I can.
- Now apply a thin coat of grease to the sealing surface of the air filter box, put the grease where the filter seals against the box.
- Re-assemble to Air Filter into the Air Box.