Been a long time since I drove one of those. I started out in a swing fender 67 C800 with a 413 in it.
The governor prevents the engine from being over revved. IIRC the 413 was pinned at about 3800. There is a vacuum pump in the distributor and it would draw the throttle blades closed when it hit 3800.
If you disconnected that hose it would rev to the moon with a similar increase in MPH.
