If you can find one of the old vibrating reed freq. meters you can set the speed by simply resting the meter somewhere on the genest. It will sense the vibrations and give you an accurate 61 Hz to set the speed.
Best of luck,
Or plug in a 110 v ac dial clock or analog into generator that side by side to your cell phone’s seconds or better yet another analog clock plug into land line power source. If generator is running too fast…it will cause the “generator clock” to run faster than land line power clock and will result a higher voltage.
Adjust your generator engine governor to slower or faster RPM until both analog clocks second hand is running the same speed or time matches. You should be in the 120 volt range after the adjustment.
All ac analog clock speed is depending by the cycle per second. Which is USA standard of 60 cycle.
Sojourn for Christ, Gerald