Help my new to me 2009 Vulcan 900 classic Lt is sputtering
So I just got my Vulcan 900 my first bike it's only got 5000 miles on it yesterday was great got it to 80 with no problems ran amazing. Today me and my fiance were on it hit 60 to 65 and starts sputtering real bad and losing power throttle down to 55 60 and runs smooth again. It also didn't want to start previously this afternoon. Thoughts? The guy I bought it from hadn't road it in awhile started it periodically. But the gas in it was old when i took the cap off it there was gunk round it. Added new gas and seafoam to it. I dont know much engine wise. Pretty sure its fuel injection does it have a fuel filter or anything what can I do?