How can I fix my 56 plate Peugeot Speedfight 2?

I purchased my moped in October and it ran perfectly, for a month or so...
then i started to need more revs for it to engage drive to set off. i thought that it may of been the rollers that were worn, i left it as i had no time to replace them and obviously the problem began to worsen. Then a couple of weeks ago my scooter began to splutter and it was really gutless when picking up speed after slowing down. At first we believed it was the fuel as id filled up at a different petrol station to what i normally use. So my dad drained and cleaned out the carb and we put new fuel in, it was no better... so when i got my Giannelli exhaust for it i replaced the rollers with the ones they gave me. it was still running terrible, i also put a new drive belt on my bike, which made absolutly no difference.
Now when i give the bike full throttle i can hold it back, it just has barely any drive, then when i eventually get it to move it hardly accelerates!
im completed stumped, i've done everything i know, any ideas of what could be wrong would be much appriciated, many thanks

Paul
January 2011