I’m not sure if you mean you rebuilt the carb, engine or entire “kart” as you said. If it was just the carb, then gaskets are most likely the problem. Take it apart, watch the video step-by-step and pausing it to confirm the gaskets are in the correct order and orientation. The needle o-rings do crack and form an angle to them, so its a good idea to replace them also. Make sure the intake block is installed the right way. There is a hole on each reed/intake block and the carb that need to match up.
You said that the engine fires up to full throttle, idle, and back to full throttle again. If the engine is doing that, how does it get a chance to get to 160 deg? Double check your water lines are installed the right way and make sure the water pump bands have tension on them, so they don’t slip.