Normally it would sound like a lean condition. It could also be a governor adjustment. I dont know that model but many small engines use very thin light springs that cover the throttle/governor links. These springs hook into the arms at each end of the link and keep the slop out of the linkage. If the springs are broke/disconnected it will usually"hunt" rather quickly but could also cause a rolling surging action.
It seems too new to have rotted fuel lines and sucking air. If adjusting the gov be very careful as some engines will expierence catastrophic damage if adjusted improperly. Not due if yours is mechanical linkage system or electronic. Time passes us by when our hands are no longer on the stuff.