Bike has 4k miles. One morning I started it up, rode about 1/4 of a mile, normal/casual shifting and throttle, and I felt it sputter and hesitate while riding in 4th. Kinda like a misfire sorta. So I pulled over, and engaged the clutch, and then the bike stalled. I parked it. Didn't ride it for a few days, then tried riding it, same thing happened, but this time it stalled almost each time i engaged the clutch and sputters randomly in all gears. Parked it. Air filter looked ok, fuel is premium from costco, crankcase breather was empty, oil looks good.. haven't checked the spark plugs or fuel filter.. any ideas what I've got going on?