As the RPM rises, the balls, which are actually weights, would move up and out due to centrifugal force and when they reached the fully up position, they cut spark or fuel, I don't recall which, decreasing RPM
at the full rated RPM, they would be sticking straight out from the shaft on their arms, giving us the term 'balls out' for wide open, that's all it's got
ah, it was fuel, check it out
https://en.wikipedia.org/wiki/Centrifugal_governorYes, I'm one of those kids that, on a field trip to an old machine shop (with belt driven tools run off a water wheel) had to be dragged away back to school, protesting every step ofthe way