It is hard to diagnose whats wrong with it over the forum. We can sit here and tell you a hundred different things to check. Give us more description.
Does the engine sound like its working really hard or does it sound loud like its a weed eater?
Details details details. If a picture tells a thousand words a video tells a million. Make a short video if you feel comfortable riding with one hand. Also make a video of it just idling on the main stand and then rev the engine a little. It's easy to start a Youtube account and post the links here.
Even with a video we still might not know the cause of the problem. I have a feeling it would be a huge help though
It is much quieter than before the power loss. I am still riding it about 3 miles a day and top speed is 18-21MPH. Between the start of acceleration and full speed it seems to miss and sputter some. Very slow to accelerate, almost have to push off with my foot to help it get going. It seems almost as if it is starving for fuel, maybe getting 1/2 or less the fuel than it needs. Also, it may have more white smoke than normal. And thanks for all the help, I really appreciate this!