Top end power loss

Hi to all & best wishes for 2011!
There's a pair of ZZR250s (both 2001 models) in the shed: Both used to pull around 160kph.One still does. However, the eldest son decided to use his one without coolant....After replacing holed radiator & stuffed water pump, new spark plugs, oil change and valve clearances, it does everything right: idle, no abnormal engine noises,and pulls cleanly through all gears EXCEPT top gear. It won't budge over 120kph.
Feels like it has a limiter on it.Any advice?
Thanks, Mark
There's a pair of ZZR250s (both 2001 models) in the shed: Both used to pull around 160kph.One still does. However, the eldest son decided to use his one without coolant....After replacing holed radiator & stuffed water pump, new spark plugs, oil change and valve clearances, it does everything right: idle, no abnormal engine noises,and pulls cleanly through all gears EXCEPT top gear. It won't budge over 120kph.
Feels like it has a limiter on it.Any advice?
Thanks, Mark