Peugeot Speedfight problems

Hello,

My son has using this ped all year, standard (from what we know) Speed fight WRC 50cc AC and it has always been fine. However he came home on it at the weekend and said it started to lose power and wouldn't run beyond 20mph (it can normally hit 40-45mph). I tried it and it runs okay at first, gets up to speed, but after a few minutes started with the same fault with the power loss and then wouldn't run beyond about 25mph. Haven't a clue what it could be.

Please help

I didn't find the right solution from the internet.

References:
https://www.bikechatforums.com/viewtopic.php?t=297720
3D animation studio

Thank you