it looks like you also have a grip of pipe tape on the threads too, a little bit is good for stopping leaks but if the metal is not making good contact (getting a good ground) it may be effecting when the fans are turning on. If your motor got that hot it might be safe to say you need a new thermo usually after they get that hot they go into failsafe and stay open.
Another thing since you say its heating up quick might be because either your timing is off or since you got a new carb it might be running too lean causing it to overheat.
Another thing since you say its heating up quick might be because either your timing is off or since you got a new carb it might be running too lean causing it to overheat.