What do you mean hitting limiter at half throttle? You should hit around 6600-7k rpm at full throttle. If you're hitting those RPMs early you have a drivetrain problem. If you aren't hitting high RPMs, you probably have an engine issue.
If you're unable to get high rpm even at full throttle, you have an engine issue. Check compression (no harbor freight gauges).
When is the last time you rebuilt carbs? Did you use genuine mikuni? Did you replace fuel selector, water separator, and the grey fuel lines?
If you hit high rpm early, check impeller, wear ring, and ensure there's no blockage or restriction in the jet path.
Also make sure you're greasing the jet pump hull bearings every time you go out.