First, make sure the oil level is no more than half way full in the sight glass (I run mine in the lower 1/3rd) after it's been sitting upright and level for 5-10 mins. It can be easy to overfill these things when changing/topping-up oil.... if it does get overfilled (even by a little) it will puke into the airbox, especially on the track.
If you are still getting oil pukage, check the crankcase vent on the back of the engine to see if you are getting standing oil in there. I like the corse style setup with the valve in the airbox.
If you continue to get alot of oil in the airbox, do a compression/leakdown test to see if you are getting excessive blowby in the rings, which will create excess pressure in the crankcase.
If you are still getting oil pukage, check the crankcase vent on the back of the engine to see if you are getting standing oil in there. I like the corse style setup with the valve in the airbox.
If you continue to get alot of oil in the airbox, do a compression/leakdown test to see if you are getting excessive blowby in the rings, which will create excess pressure in the crankcase.