it could perhaps be rad weld that the previous owner has rut in to sort out a leak as this is what i found in my sisters car after putting in radweld to sort a leek out.
try running the bike with a dry air filter or a filter with very little oil if you dont fancy that.i own a 94 kroo it used to do that but did what bill pye said and it worked.good luck.
try running with a dry air filter. i own a k roo and used to have the same problem. sounds like a strange idea but bill pye told me to do this. not sure about the fork oil levels.the fuel mix is what i use in my fantic and it goes.
