You might be running too lean, either from too small jetting, or a possible air leak. Both of those can make the engine run hot from a lean condition, requiring a cool down.
Do a plug check. If you want us to help, run full throttle for a block or 2, and keep it at WOT (wide open throttle) the entire time, and throw the killswitch while still pegging the engine. Take multiple pictures at different angles showing us your plug, bonus points if you actually chop the plug with a hacksaw or at least shine a blindingly bright light showing us colors down the electrode ceramic down to the bottom.
I advise not doing it like me. I use one plug, and risk massive failure by cooking my new plug to the new settings
.
Most pros will use multiple new plugs to tune their jets.
I just test a mod about a quarter mile, and only finish it if it didn't feel wrong. I then pull the plug and see what color change it gained. Even though it is a used plug, I can see if the engine ran richer or leaner during that run. I know my plug like my third leg. I have a micro drill bit set and a solder gun with solder. Never had a single issue with jetting.
The 3 biggest things I see almost everyone have the biggest issues with on kit or custom motorized bikes: jetting, gearing and alignment.