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The htz can be adjusted by the governer on the side of the engine where all the injection lines come to the injection pump. On the pump will be a little lever held in place by two set screws. Put a htz meter on the output and set the engine rpms (1800rpm) so you see 61htz no load on the meter. Full load will normally droop to 59htz.
The volts is another issue. That is set by the voltage regulator by means of sending voltage/current to the rotating field. Running up the htz won't fix the low volts. Set the htzs first then set the voltage regulator to 120v at the voltage regulator board. This is more complex and often a low voltage needs a tech because the low volts may mean a winding is failing. If the voltage going to the field is over about 3v under no load then the winding is suspect. 12v will be max voltage at max load to maintain voltage.
Let me know how it goes.