Check the triple clamps and steering stem to ensure everything is tight. If all is okay the fork is probably to stiff or the rebound too slow. Honda recommends after every ride or about 2.5 hours. Thoroughly clean the filter with a good cleaning agent designed for filter cleaning, or use mineral spirits. Do not use gasoline.
Gasoline tends to dry out the filter and can dissolves the glues at the seams of the filter.
After cleaning the filter, rinse in with plain old dish soap and water. Allow it to dry completely. Apply air cleaner oil to the entire surface of the filter, inner and outer. Rub it with both hands to saturate the air cleaner with filter oil. Squeeze out any excess.