I had a similar problem with the overflow bottle on my 99 220, I took it off and run without one, after the raditior blows the first 1/2" of coolant from the top the problem goes away. if the head gasket is leaking as mentioned above the problem will be there all the time, if you hold the engine at 4000 rpm'ish water should be running out of the overflow tube fairly constantly. another thing that helped my bike was engine ice, it pretty expensive, $15 for a half gallon, but it works pretty darn good. if you can't find it at any shops in your area email me and i'll let you know where you can find it. another thing, when filling the system pull the 10mm bolt out of the neck on top of the head, this will let air out of the cylinder while the coolant goes in, and don't use straight coolant or it will run hot.