Are you sure it's the heat and not simply that the engine has been running for awhile? RX-7s are notorious for not starting easily when hot, but the problem may simply be that it is flooded. I.e. when you shut it off it did not burn the fuel already in the chamber and/or your injectors leak a bit. I always kill the engine by shutting off the fuel pump and allowing it to die; that way all the fuel is used up and you are not trying to start a hot engine that is overly rich. If you have your fuel pump switched, try that. Otherwise, try Scooter's remedy.