The book says 10w-30 or 10w-40 JASO (safe for wet clutches). I've always ran 10w-40 in my Hondas so that's what I went with. I ran regular GN4 Honda 10w40 for the first 2 oil changes (I did 100 miles, and then 600). When I hit 1800, I switched to the Amsoil 10w-40 UTV/ATV oil. Haven't had any problems.
On my 500 that I used to have, I switched to Amsoil at the first oil change I think. I was very meticulous about oil changes between 500 and 600 miles. After a couple thousand miles, I began having oil consumption. There are theories that if you switch to synthetic too early, the rings won't break in enough and that can cause oil consumption. I'm not giving advice about that because I really don't know. But that "theory" seemed to match up with my situation before.