After exhaust change, scooter no longer starts

Hello guys, I have changed the original exhaust for a Tecnigas Silent Pro at my Speedfight 3 LC. I have changed because of a problem that I have had for weeks, if the scooter is cold, I can drive about 3km without problems, if I have to brake because of traffic, e.g. at a traffic light, the scooter drives only 20-30km/h, the same happens with stronger climbs, the scooter then stays at 5500-6000 turns and does not come higher. Sometimes it comes after a few hundred meters then again higher, sometimes not. I guess it might be on the exhaust and have changed it today, but now the scooter doesn’t even jump on, what can it be? MfG Arne