the manual says 25 hours for first change and valve adjust at that time. When i went thru service tech training class, they recommended no later than 1st year for valves and oil and filter change. problem is that after 1 year, most generators only have on 8-10 hours on average. my training technician recommended following generics opinion to change it after first year even if the hours are low. i have noticed that approx 25% of the units i service in 1 year have needed minor valve seat adjustments. a few were severely out of wack. after the first setting, ive very rarely had to reset them a second time, but i do check them after every 200 running hours.
ive checked a few that were brand new out of the crate just to see , and they were both spot on. i guess its just the nature of air cooled units that dont have hydraulic lifters to keep an eye on them.
on my own unit, i will check them every year, and i change oil every year. im scheduled to do mine this weekend.
when checking valves....ALWAYS MAKE SURE ENGINE IS COLD. Never adjust valves on a warm or hot motor.