Most likely your bike is overfilled with oil.
It can be tough to get it correct.
No more than about 5.5 quarts on refill
or it starts blowing the excess oil out
into the air cleaner from the engine breather.
This air is the pressures inside the engine
when it's running. It needs to vent the pressure
and there is alot of oil mist in there as well.
Worn rings can increase this problem but all
engine have some pressure and blowby.
A solution if lowering the oil level does
not help is this Krankvent vent: