Good advise above +1 for LO206. I would add that rebuilding an engine takes more than simple hand tools. When looking at used karts make sure the brakes work first or at least check to see if you can get parts for that model brake system. Systems change every couple years then you can’t get seals, pads ect.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience