Re: Quieter muffler?
Other ways to quiet the bicycle motor kit are to-
Place rubber blocks between the cooling fins on the head and cylinder.
If you experiment with a better air filter/box you could quiet any two stroke nicely.
Make sure you have proper lube and tension on your drive chain-3/4".
Secure all "sheet metal" such as fenders, chain covers, reflectors, seat springs, or anything else that can vibrate and make noise.