I've replaced the fuel pump with a new Airtex electric one. The coil is a new Bosch Blue, the ignition is Pertronix. Wires are new. This seems like a vapor locking situation. The carb is a Weber DGV. The car runs great into the N zone of the temp guage, then begins to stumble a little. Then it is impossible to start until the engine cools down. This is a 74 1/2 MGB GT. Any suggestions?