Dluberk

Greetings. I am a new YBR owner, bought a used carburetor (2010) version. All was running well with stock engine until I decided to do a major DIY which was to upgrade to a big bore 150cc piston set. I did everything as found online (placing of piston rings, timing marks aligned etc.) and the engine starts and runs well initially when cold. But when it gets hotter with running, it tends to die to the point when it will not start again no matter how hard I crank, until it cools down again. Can anyone advise the solution pls? Thank you