why wont my peugeot speed fight 2 go properly!??? :(:(:(?

hi ive just brought a peugeot speedfight 50cc with a 70 kit on it first day when i went 2 pull of it just wouldnt! entill i tried again 2nd day pulls of very slowly with huge moan but it wont go any faster than 40kmh without sounding like its in the wrong gear even if it doesnt have any. i contacted the kiddy i brought it from and he reckons the rollers were shagged could this cause wat i have described cheers :) thanks for your time