Guessing I'm after a carb rebuild with diaphragm? Have seriously considered a KLX kit, but I'm not power hungry on this bike. I dig the range 45-50 mpg gets me.
Any aftermarket muffler can not Muffle
the trailing throttle after-fire as well as the oem muffler will.
A loose exhaust header pipe or damaged header pipe gasket or crack in the header pipe will cause more & louder after-fire / popping.
A rotted/damaged/sticking idle air cut-off diaphragm will cause more & louder after-fire / popping.
The 22 cent mid-range needle shim mod or the KLX mid-range needle may alleviate your mid-range steady throttle intermittent hesitation.