I recently got an Fa50. Mine was in poor condition. The power sucked. The muffler on these can get pretty clogged up. When I took it off and looked in on the cylinder. There was a wall of black carbon crud blocking the exhaust. Check these things and see if that helps. I also ordered a tapered plug from the local auto shop. About 2.25 but it was the one that the book said that it was supposed to have. Check the crank case also, people sometimes tend to think that it is supposed to be full and fill it to the top. You may also check the compression.
The guide that is posted here is a lot of help.
As I said, mine was in poor shape mechanically when I got it. The jet is a little too big and it will two stroke when it is about to wind out. Cleaning up the exhaust really helped everything out.
Good luck with you new shuttle. I have enjoyed mine. I can't wait to get a differant moped though. After reading about all of the comments here, I think that I want an old Puch or Tomos. Parts from the Suzuki dealer are rediculous. I had to replace the needle valve in the carb and paid 35.00 for something smaller than a dime.