What is the best way to clean the air filter?

 

They make air filter cleaner in a an aerosol can.I use Klotz Air Filter Cleaner.

Fabric Filter (like K&N)
Remove your air filter spray it on inside and out about 1/4 can or so let soak for 1-2 minutes.Spray from inside to outside with garden hose (medium pressure).Let it air dry,compressed air can tear the fabric.Spray on the Klotz Fabric Filter Oil.Let that dry a couple hours.

Foam Filter (like Uni or most stock)
Remove air filter.Remove the foam element from the frame,if you can't, throw it away and buy a reusable airfilter.Spray it good with the cleaner,squeeze it,spray again.Let it soak 1-2 minutes.Wring out under running water.Let dry.Spray on the Klotz Foam Filter Oil and saturate it,squeeze out excess.Reassemble foam on the frame.Let dry a couple hours.

Paper Air Filters
Replace with fabric reusable units.

It's best to have two airfilters then you can service one the right way and still have a clean one to ride with.
Hope I helped.

'88 250R many extras

 

I have a stock filter which is yellow and after my last two rides it has now become black so i figure its time to clean.

 

I have used PJ1 Foam filter cleaner spray and PJ1 Foam filter treatment spray(super tacky) for almost 4 years now.(used to do the diesel fuel/engine oil soak method) For the best results I follow directions on the can. I two have two sets of filters for my Raptor and Kdx200 because lots of times they need cleaning from the dust and then I can throw a new set of filters on so the machine will be ready to go for the next day. Many a night after cleaning the filter for my Recon I have set at the table with a hair dryer(high heat) so I can get that filter back on. Depending on the machine if it has a sealing ring be sure and put extra filter treatment or some hard grease to prevent dirt entering the area around the ring where it seats.