New rollers v-belt HELP!

Hi all, i have recently bought a used runner 180 sp and the previous owner had replaced the variator and v-belt with malossi. The problem is after i serviced it at my local dealer where he replaced the v- belt and rollers with the same weight( the same product codes) the acceleration has dropped. It kinda feels like as its launching a little bit slower and i can feel that. Please can anyone give some advice why is this happening. Can it be because the previous rollers were worn out thus decreasing their weight and as a result the acceleration? Thank you in advance...
p.s
sorry for my bad english