So here is my rather weird problem that has me pulling my hair out. My bike ran fine for about 1200 miles after buying it from my friend who had had no such problems in the five years he owned it. Then, it got hot and started to boil. Fine, so I pull over, let her cool and throw some water in it to get it home. First thing I replace is the thermostat... still getting hot. So I take the thermostat back out and go without... still getting hot. Next I take all the plastic off and drain all the coolant and pull apart the water pump. Looks fine to my eyes, and its a pretty damn basic pump after all. So then I go out and buy some clear plastic hose and stick that between pump intake and radiator output to check for flow. Can't quite get the angle right to rid the tubing of all bubbles, but sure as heck looks like she's pumping plenty of water. So now I am stuck wondering is it a pump problem, gunk in the radiator, or something else. If it was head gasket, I would be getting coolant in crankcase, oil in coolant, and/or be smoking white like a steam engine. I am really hoping to not spend too much $ without actually fixing the problem. Pump is around 150, and I have no idea on the radiator. I don't know if I even want to mess with it if it is an engine problem. Please help if you have ever heard of anything like this before!!!