What would cause oil to blow in air box could bad valves cause this
This is a common occurrence with all Kawasaki V-twins prior to 2012. because of how the crankcase vent is designed it will blow oil or oil mist into the airbox during wheelies, long high RPM hill climbs, or in some cases long periods of high RPMs like road runs. It can also happen with excessive blow-by when the rings are bad or of the oil level exceeds the high mark on the stick....and that can happen if one blows a head gasket and coolant gets into the oil or it gets overfilled somehow. Otherwise, most have put catchcans on theirs to stop this from happening. There's a How-To I did many years ago in Brute Tech...although I think the photos are gone by now. The reality we found over the years is that all you need is a second vent "Ted" into the first vent that cones from higher up in the engine like off the valve cover plate or one of VFJ's cam plug ports and all that stops no matter the reason.