According to the Dave Danielson, whos head of the warranty department, they DO NOT RECOMMEND full synthetic oil. The engines were NOT designed for full synthetic, and a full synthetic oil can actually wash out the internal bearings and destroy the motor. A Synthetic Blend is fine, but they do not want full syn in these motors. They arent Vipers. They arent Corvettes. They arent high performance engines that were designed for it.
With that being said, I recommend at minimum a 10w40 oil. With the 500 H.O. there is no wet clutch, so a wet clutch oil is no needed. How ever, run it anyway!!! Wet-clutch oil has extra anti-wear additives! I personally run Shell Rotella 15w40 in my 800 because of the antiwear additives and the zinc in it.
First oil change do around 200 miles, after that, every 600 OR if youre a light user (less than 600mi/yr), MINIMUM once a year.
The manual will say you can go longer, but no thank you. Small engines run hotter and work hard. They arent like car motors.
Not to mention, a good grade 10-40 is around $6.99/qt and a filter is $9.99 so its not like its breaking the bank every time you change the oil. Oil changes are much cheaper than replacing a blown motor.