The manual for my FX730V said the first oil change should be done at 8 hours.
Went with straight 30 wt and new filter, I'm on a yearly oil change because I don't get the hours mowing all summer.
Change oil and filter every spring.
Dealer recommended 10w-40 Kawasaki oil witch is a semi synthetic, but not sure I want to go with a multi grade oil in an air cooled engine used in the hot summer.