Its quite complicated but simple to rev it out of gear ,if that makes any sense !
When in neutral you cannot rev the engine as a cam reduces the revs to tickover.You can set the lever half in gear and the gearbox "paddles" the shaft, this allows you to reach a point where the revs go from tickover to full within a couple of MM adjustment.
Ive cleaned the injector, numerous times, refurbished the one way valves in the supply line and cleaned the pump.
The only thing I havnt altered is the spring tension on the govenor.I think Ive nothing to loose so that is next.