The above comments are good, but if you pull the gas tank I'd first check the air filter. This time of year is when mice are building their winter homes and your air box is a great location. A nest will do a pretty good job of restricting air flow, starving the engine from oxygen at higher RPM's.
2009 Wee Strom ABS (current)
1987 Harley FXR Low Rider Sport (current - with 206K miles)
2009 Aprilia Mana 850, 2006 SV650, 1984 Yamaha Virago 1000 (all sold)
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Wee Farkles: Russell Day Long Seat, Madstad with Moose Adventure Shield +4'', SWMotech Centerstand, 1'' up & back bar risers, Givi XS308 Tankbag, Aprilia mirrors, Framesliders, Fenda Extenda, Elka Shock.