If this critter is variable speed (inverter) changing the load (speed) after an hour is universally recognized as offering the "best break in". Even Transamerica DeLavalle, who make ships engines and Pielstick of Germany recommend varying the engine speed during break in. My dad used to haul me off to various shipyards and vendors where my inevitable 10,000 questions (at age ten) sent people scurrying off.
IMHO engines do have a favorite spark plug brand. Visit some Yamahahaha forums online and see if you can pick up some tips. Nothing like a lot of comments from actual owners. You do need to weed through the duff, but using wisdom and common sense, forums can be informative.
