my GPR is about 14 hours old and due for the first service next week, i have noticed that at about 5-10 knots, with the throttle just open the motor sounds as though it is cold and has just been started, this goes away as soon as i get the GPR going ?. I am not sure if this will be solved when they change the plugs at the first service.

adjust your idle speed while in the water to 1350-1400 RPM