The recommended oil is Honda GN4 10W-40. Like Pain stated, most automotive oils have friction modifiers that will cause the clutch to slip.
Let me know if your ATV is 2wd or 4wd and I will post a link to an owner's manual that you can download.
Let me know if your ATV is 2wd or 4wd and I will post a link to an owner's manual that you can download.