I have 3 MGs the MG10MT, MG10TR, and MG16

Im having a strange problem with the TR that has been going on since I got it new. It will run fine for about 5 minutes and once it gets up to operating temp, 220 or so, it will shut off and not restart until it cools. It seems that the fuel line stays solid with fuel until this condition starts and then its all air in the line. If I blow through the pressure fitting to bring fuel to the carb, it instantly drains back into the tank.
I dont have this problem if the engine is cold.
Any ideas?