If your 650i is the same as my 750i, and I think it is, the front of the air box (as you sit on the bike) has a hole that allows fresh air to enter the airbox and cvt clutch intake. The situation of that airbox opening allows for steam to enter as well.
For example if you are trail riding along like normal and then come to a puddle on the trail. There is no reason not to go through it, it's only 6" deep. So you hammer down. But when you splash water up onto the front cylinder exhaust pipe, it instantly turns that water into steam. And if you are going just the right speed that steam will rise up and when you throttle up your engine takes a bug gulp of steam instead of the fresh air it needs.
A good friend of mine had this happen to his 08 Brute 750 a handful of times then we read up about it on the net and installed a Mud in my Blood designed, home made snorkle kit. By then his Brute had 800kms on it and was using 1/2 liter of oil per tank of fuel. We snorkled mine up the weekend I brought it home and I have had zero oil consumption in 2500 kms. Coincidence? Maybe. But too many other guys are having problems with steam to ignore it.
For under $100 of abs sewer pipe from Home Depot or wherever, it is cheap insurance like you said.
Hope this helps!
