Peugeot Speedfight 2 50cc?

I have a 2005 peugeot speedfight 2 silversport 50cc i put a tecnigas performance exhaust on it and it made it go a bit faster but sometimes came up to a junction and roundabouts after you stop bike wouldnt move and just bog down and take ages to go but when i put the standard one on it was fine, will this be because i didnt rejet the carb? and what else should i do it to it to get it to work?