+1 on gas cap vent problem.
The gas cap has small
o-rings "2 orange rubber vents" that harden and/or break, resulting in vent malfunctions.
In my case, the cap refused to vent and when the tank was mostly full of air, in hot weather, the fuel tank would become over-pressurized, resulting in fuel flowing into the airbox. Manual venting of the gas cap (when it was low on fuel, in hot weather) helped me finish the other 1500 miles of my trip.
I just checked the fiche and no Kawasaki parts appear inside the gas cap section.
Finding fuel-resistant o-rings in the correct size might work but I haven't experimented with them yet.