I think I might have found the answer from the following post by Psyco on another thread.
"If it is the thermostat type engine, then nothing will come out until it gets up to temperature, allowing the stat to operate. And then you will only get a dribble, compared to a powerful jet that you get on normal 2 strokes."
I'm hoping this is the case with my engine, it's a 2011 model but I don't know if it is fitted with a thermostat. If it is, then that would explain the erratic water cooling outlet.