Hi Greengrass,
You say the throttle only compresses the spring when applied. That's correct.
The governor on these Petters engines works by creating a balance between the governor springs in the engine and the spring you see externally. I'll try to explain.
As the engine picks up speed the governor weights which are mounted on the cam shaft gear in the timing case are held in place by the governor springs. They fly out by centrifugal force as the engine speeds up overcoming the springs.
The weights are linked to a rod which passes through the hollow cam shaft and exerts pressure on the governor control arm, (lever), at the flywheel end of the engine as the engine speeds up.
This arm in turn then pushes the injector pump rack back cutting down the fuel supply to the injector and so slowing the engine.
The external spring compresses against the opposite end of governor control arm as the accelerator is applied. This exerts increasing pressure against the control arm overcoming the pressure exerted by the governor springs until a balance is achieved.
The engine then runs at constant speed according to the pressure imposed on the external spring by the throttle pedal.
I don't know if you can follow that, but I tried.
