2008 speedfight 2 problem and tuning

HI all. hoping someone can help me im completely new to all this and need some info.
ive had my 2008 speedfight 2 for a couple of weeks now and im loving it but it seems like it is having trouble accelerating at higher end and also sometimes pulling away from junctions it will struggle and judder, almost like its struggling for air or fuel. the ped had a gianelli exhaust on and previous has told me it has not been upjetted.
ive now been looking at a malossi 70cc kit
a pack of jets (need help with which ones)
a 17.5mm carb (again need help with which one)
what else would people reccomend for a reliable but reasonable speed ped!

any help massively appreciated