I had twin Suziki 115's on a 2650 Pusuit I used to own. There is a difference in oils I recommend staying with only one type of oil. When I switched I fouled the engine and constantly clogged the screens. I flushed the entire system out and only used Yamalube afterwards and never had a problem again. Any name (major) merc, Johnson Yamaha brand will surfice. I have a two stroke motorcross bike and would never mix with synthetic. Synthetic oils do not burn well and leaves residuals. I just read up some more on Synthetic oils and they look fine. I have 100 hours on my motor and would not switch. I do know dirfferent brands have caused me an issue.