I don't think there are too many Onan generator techs on this forum, but I may be mistaken.
As a suggestion, contact your nearest Cummins/Onan dealer/repair center and ask them your question.
Link to their website for dealer/repair locations...
There may also be a downloadable specs sheet or manual available for your specific year/model generator at that same site that might help.
Found this old thread on another forum, with some references to governor settings. Maybe there's a clue in the discussion there for you?