Have a buddy who bought a used yz125 for his son.
The bike bogs in 1st and 2nd gear then in 3rd runs ok. He walked it out 3 km bike died. Took plug out when he got home and it was completely burnt out.
Has happened a few times now.
Just wondering what would cause that
A few ideas
Fuel / 2stroke oil mix?
Fuel / air mixture?