these are prone to heads warping ,does the radiator bubble if you have the cap off from cold and then run it for a few minutes.if it looks like a little jaccuzi in there then the head gasket is leaking more then likeley due to a warped head.ski it and refite it using a new gasket and it will be ok also throw the thermostat away while you doing it to let the coolant flow better,it may take a minute longer to warm up in the winter without it but its a small price to pay for better flow and not having the risk of the thermostat packing up and boiling your engine up.
adam bike doctor, March 2010
