[Rich Biebel]

Engine rpm is read with a Frequency counting volt/ohm meter.
62 Hz no load
58 Hz full load

And yes that is basically 3600 rpm all the time....each 1 Hz = 60 rpm of the engine
The generator end/rotor is spinning at the same speed as the engine and the AC frequency indicates engine speed..

That’s ideal numbers and the governor controls that.
Flyball type governor inside engine attached to the arm on top.
Spring tension and arm leverage are adjustable.
There is a low speed screw that may be interfering with governor arm action.
It’s on the carb and you should be able to pull on the governor arm and lower the engine speed.
If it does not come down some that screw needs to be backed up a little.

That’s the usual scenario when engine speed does not move much.
It usually causes them to overspeed once load is removed or at least it can cause that occasionally.

There really very simple but complicated ! Lol