expansion

My 66cc motor won't hardly run with the stock muffler, when I take it off it runs like a champ. Anyone have bikeberrys expansion chamber with muffler? What do yo think of it? How much louder is a regular expansion chamber?

So i came across this exhaust system in my Frantic searching after my Modified pocket bike exhaust ''Expansion chamber'' cracked at the header, Due to my bending it too fit by force no map gas lol So i went on a search for expansion chambers and since last time i bent the header too fit, it...