Harley routes your engine breathers into the
air filter so the engine can burn the oil mist
created in the engine.
This is to reduce emissions.
The oil mist often does not burn fast enough and
so builds up in the air cleaner over time and
You can clean the air filter, check the breather orings
in the air cleaner, reduce your oil level as
the bike might have a bit too much oil in it
or install a breather bypass and route the hose
to a little filter near the ground to get rid
of the problem. Bike might even run better
without all that oil mist.
Example of a bypass kit, there are others: (Cut/Paste)