MG Car Repair: fuel pump, fuel hoses, vapor lock

Question
Have a 1976, MG midget, 1500, it runs great but I noticed this summer a few time after driving in the heat it would cut off on me and refuse to start until after it cooled down, sometime hours at a time, during the time it refused to start I took the fuel line loose at the carb and turned the motor over , no fuel would come out, I thought it had vapor lock because after cooling it would start,,,,,,, it did this one other time during the summer but them in the Fall  during a cold evening it happened again, cut off , not fuel to carb......I don't think that would be vapor lock, I have a manual fuel pump,,,, getting ready to replace pump,, what do you think ?

Answer
Hi Steve.  You are not the first person to contact me with these symptoms.  I have a theory that the problem lies with modern fuel containing Ethanol.  Engines with a mechanical pump seem to be worst affected, whilst those with an electric pump outside the engine compartment are least likely to be affected.  

Before you do anything else, check the pump when the engine is COLD.  If it does not deliver a good strong supply of fuel, then the pump has failed, usually with a split diaphragm.  

If the engine starts OK but dies after 2 or 3 minutes, then the problem is probably icing-up of the carb.  This can happen even if the air temperature is as high as 70F, but is more likely on a cold, damp evening.  

If the problem only occurs after the engine is thoroughly warmed up, then the fuel is boiling before it reaches the carburetter jets (this is known as vapour lock).  This could be the pump getting too hot, or the fuel hoses, or the carburetter float chambers, or all 3.  In this case, I would fit a heat shield (unless you already have one), blank off the hole where the mechanical pump bolts to the block, and fit an electric pump at the rear of the car.