If it was a head gasket I would imagine that some of your water would be going into the oil. If you don't see yellowish white foam anywhere inside the site glass or at the top of the oil fill then I doubt you have a head gasket problem. There maybe a line not totally tight that you can't see. Or maybe the over flow is leaking. Is the bike getting really hot? Maybe your water pump is not working. I'd check out all thos things before even thinking of head geakets.