From what I could gather, it sounds like a tired motor. Pull the rotor cover and wiggle that puppy, if and up down play, its the big end bearings, side to side is ok. Next get your shop manual and do a top end, don't scrimp, purchase everything, install em correctly and torque it to specs. Hint never use gasket sealer, and carefully clean all mating surfaces. Clean and oil that air filter. Buy 91 octane gas and mix it correctly. buy a fresh ngk spark plug and go from there...