take off exhaust pipe and look inside the exhaust port how much carbon inside especially on the valves flaps . if you find much , it's time to decarbonize and change piston-kit .
if ok i suggest good cleaning on :
- tank and tap (fuel filter)
- air box foam filter
- carb (strainer and float chamber) and blow all the jets
- gear box oil change
- oiling on every cable
- break pads check