i just bought a 400ex, when looking it over today i noticed that the air filter was really dirty and dusty no oil at all on it. what is the best way to clean it?

 

I use the same K&N filter cleaner and oil that I use for my Jeep. Those are K&N filters, but I would have to guess that would most aftermarket filters. If it is a stack filter I guess you should buy a new one. They are not that $$

 

Foam filter use dish soap and water.

 

I agree with xcitmt.