You'll get different answers - there have been several threads on this. But my 650 runs fine on any of the octanes. I usually run the 87 octane regular. The 89 octane ethanol spiked fuel is actually a bit cheaper in this state. I usually avoid it for both my cars and motorcycles though. The manuals all say you can use it, but I am unsure of the long term effects of running ethanol through the fuel injectors & engine. A minority of riders do believe that they see a small increase in performance or mileage with higher octanes, but I haven't seen that myself.
The factory service manual states: "Use only unleaded gasoline of at least 87 pump octane (R+M/2) or 91 octane or higher rated by the research method. Gas containing MTBE, less than 10% ethanol, or less than 5% methanol with appropriate cosolvents and corrosion inhibitor is permissible."
I use 87 octane and the 650 runs just fine.
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