Engine problem XL350R

Hello together, A buddy of mine has problems with his XL350R: The mixture overgreases when the engine is really warm, the engine is stuttering and the candles are rusting. We have already disassembled the carburettors (which is why the vulture needs 2 carburettors …), cleaned (into brake cleaners and blown out with compressed air) and re-set. We have also hung the nozzle needle a little deeper to make the mixture leaner. After the assembly, the box only runs completely n ormal, but if it’s really warm then the game starts from the beginning. Has an XL350R driver ever solved a similar problem? Or does someone have an idea what could be lazy? We are grateful for every tip and every help. Ciao, Harry