If I were you I would take the carb apart and clean it. Take the airbox out and clean that too. New filter,new oil and new spark plug,lube up chain and cables. Begin on your terms. Repacking the muffler is exactly like repacking 2 stroke muffler. Pop the rivet off and repack. Then rivet back on. If your looking for significant horsepower gain then thing again. This bike is a slow steady work horse made to climb trails not a speed performance bike.