When I start my 650 with the air filter off, I seem to have alot of air flow coming out of the crankcase vent tube. It actually blows out of the tube. Does anyone else have this happening to them?
Hope it's not the rings.

 

It does it on all of them some, the bigger the motor the more air comes out of the breather tube. The reason it does it is because when the pistons go up it pulls air in the case ( a vaccum action ), when the pistons go down it forces the air out of the case, that's why it's located in the air box so the air is filtered to the crankcase. My XR600R I had would do it so bad that you could hear it, also when I took the lid off and put in a K&N filter the air noise in the airbox was as loud as the stock pipe.