Scooter not getting up to speed?

Hello everyone, I installed a new exhaust on my Peugeot SpeedFight 3 AC scooter (Doppler exhaust). I also tuned the exhaust in the clutch using a compression spring and clutch springs. Acceleration was good so far, so I tried tuning the scooter with weights. I tried the included weights (from the exhaust), but it didn't help. I tried heavier weights again, but unfortunately, nothing helped. I then tried again with weights, but unfortunately, nothing helped.

Maybe if it helps the scooter gets up to speed up to 30 KMH then it stops and then very slowly in 1 KMH steps it goes forward

and the scooter now only drives at a maximum of 40-45, although it used to drive at 55-60

maybe someone knows what the problem is

LG