What is theoil weight for a 2003 Yamaha 660 raptor?

Depends on where you ride, the numbers mean thickness and it depends on temp. Lower the first number the easyer it starts in cold temp and higher the second number the better it can stand high temps. A good 0W-40 or if you dont live in a cold place 10-50 should do a little better. I run Amsoil 0W-40.