Thanks for the prompt reply.
I have read the workshop on how to set the power valve. Maybe my description was a little long and possibly confusing. I was trying to get across that the servo does exactly opposite to yours and the workshop description. In that, at switch on, nothing happens. At 2000 rpm the servo operates and just above 2000 rpm the servo closes and remains closed no matter how much the rev's rise. I hope this clarifies the situation.
Thanks
Alan