Gasgas ec 300 2015 not reving

[eralha]

hi guys, i have a friend that have a gasgas ec 300, and after last ride his bike started to have some trouble reving, it will not pass the middle rpm's to the higher.
Seems to me that the bike is running to rich, i have a 2018 300 and we swaped some components from my bike to theirs just to see where the problem is:

- ignition coil
- reeds
- carburator
- central control unit
- spark plug

If i open the throtle, or try to rise the front wheel it start's to boggle, but if i give throtle gently it will rev to the higher rpm's.

Nothing seems to make a diference on the bike, it have new piston and rings but this problem happen before the new piston. where can i look more? The stator?