i just bought a used yfz450 and am getting ready to do the first oil change and was wondering if it is ok to use another oil brand because i do not know what the previos owner used for oil

 

Yes, you can switch oils. My opinion would be to run the amsoil 0w-40 4stroke motorcycle oil. It is a full synthetic oil, runs about 7-8 bucks a quart and is an exceptional product. I run it in my raptor and I am very pleased with it. The engine runs cooler and the clutch grips better.