Thanks heaps, I will try the filling up procedure next weekend. Does it normally expel the water when the engine is running or when you switch it off?
Just not sure why I can drive it for 30 minutes with no issue, stop and check it and its OK. Then at some time after that seems to have the issue. Its as if the temperature is slowing raising up, maybe its just a radiator cap. What pressure cap to you fit?
Interesting the manual also gives reasons for overheating as "ignition too far retarded" and "incorrect carburettor adjustment". It is missing under load at the moment and I have a intake leak on one throttle of the carbie too (which I cannot find ).
Running a coolant in it too, I will flush out as you suggest. Thanks for all the suggestions there, experience is always worth is weight in gold.
Not sure about the scoop, will have to have a look.