Thanks for all the great comments.
The bike is a Huffy cruiser bought at Wal-Mart. It originally had fenders and white wall tires. The engine kit (55cc) was purchased from Simpson motorbikes. I bought the muffler used from a local scooter dealer. I think it might be for a pocket bike, but I’m not sure. I hacked the original muffler off and attached a pipe to extend towards the back and attached the new muffler. I think it’s quiet as or quieter than the original. It definitely has more power. It did run lean with the new pipe even on the richest setting. So I put a few small washers under the c-clip to raise the needle and it was good to go.