Unfortunately, there are a few moped exhaust pipes which are prone to losing their baffle over time. The following article describes how to easily make a replacement baffle for said exhaust pipes. In this particular case, I used a Tecno Bullet pipe but the method can be adapted to many different exhausts.
All you will need to do this is some muffler packing (available at many auto parts stores and almost every motorcycle shop), a hose clamp, a soda can, a hammer, a nail, and some bolts.
Before you buy the soda can, measure the diameter of where the muffler was once connected (for reference, the Bullet is a 56mm and the Tecno Circuit is about a 48mm). Then, go to a grocery store or any type of store that has lots of cans with a set of calipers and find the can with the closest diameter (cans are so thin that even one with the same diameter as the end of the pipe should fit).
Cut a piece of muffler packing to fit around the rod running through the middle of where your muffler used to be.
After enjoying the beverage of your choice, cut off the top of the can. Next, carefully and gently (it doesn't take much) punch out a hole in the middle of the bottom of the can using the hammer & nail, and then the hammer & an m6 bolt, and finally the hammer & an m10 bolt.
Slide the can on to the end of the pipe.
If desired, paint the new baffle with a high heat engine enamel purchased from an auto parts store.
After letting the paint dry, slide the hose clamp over the can so that it can tighten down on the metal of the exhaust pipe. Tighten the hose clamp and enjoy a somewhat quieter moped.