I switched to synthetic after 10 hours. Now have 21 hours on it and all is well. I do not think it takes the full 20 hours to seat rings now days. I use Red Line Racing 40wt, it's for race cars, but I called the Red Line factory and asked for a recommendation. They said they have several motocross teams using their Racing 30wt with great results. The guy at Red Line said that since Yamaha recommended 20w40 for my '07 to stick with the Racing 40wt, which is a 15w40. I think engines make more power with lighter oil, so I'd recommend Amsoil 10w40. I know the Powersports 0w40 is good oil, but I'd shy away from any 0w(anything) in an engine with a wet clutch. To get the 40 viscosity range an oil must contain lots of viscosity index improvers. These VII molecules are long chains of atoms that uncoil as heat rises to thicken the oil. The problem with these relatively large molecules in our application is that they tend to get sheared badly in the transmission and wet clutch. The closer the two numbers on oil, ie 10w40, or even 10w30, the less VII in the oil, as a general rule, the less it has to shear down and degrade the oil. If you'd care to run a straight weight oil like say a 40wt oil, they have no VII and would tend to last longer. In reality either Amsoil will be fine, just change it every 10 hours or so if you run it hard. I like the Mobil One Racing 4T in 10w40 also and will probably switch to that when I run out of Red Line. Also Maxima is out with a new 5w30 oil that looks very promissing. If I get the nerve to go lighter on viscosity then this is the oil I will try. Sorry for the long post, but oil is one of my "things".
