its high time u change the oil...... never keep the same oil running in ur engine for sooo long...max is three months... ahh ...as i remember , u already tried jetting and u screwed ur carb setting and stuff right ?

better leave the carb alone for now.. the thing is its simple psychology.. i got a k&n filter from my frnd for my cd 100... my first bike... i lived with the roaring sound for like 2months.. then got fed up..