MG Car Repair: Follow up on MGB stops when hot, rubber diaphragm, bio ethanol

Question
Hi Barrie, some additional feedback. I reinspected my fuel pump diagram, turns out the only element with a tear was the clear plastic disk (maybe .003 inches thick) over the rubber diaphram. I got a new diaphram from Moss and it did not have the plastic disk> I'm guessing maybe the plastic disk is to prevent the rubber from being attacked by 10% ethanol in gas. Anyway I reassembled the pump with the original diaphram and cleaned the contacts-again! Ran a flow check and was getting a full pint in less than 30 seconds, compared to 1/4 pint previously. The pump sounds a lot "stronger" as well. Did a road test and the car ran well, no problems. So I suspect the problem was fuel starvation from the beginning. We'll see how long the pump stays strong, although I do have a solid state SU on order to avoid contact issues. Thanks for the help- Peter

Answer
You're Welcome, Peter.  

In the mid 1970s the SU pump gained a plastic membrane to protect the rubber diaphragm from the additives which were used when unleaded was introduced.  That membrane must not have a split in it.  Modern replacement pumps use a flexible plastic diaphragm that is claimed to be impervious to today's fuels including bio-Ethanol E10.

Whenever you get in the car, just listen to the pump and allow it to stop before you hit the starter.  If it gets a bit lethargic, don't immediately assume that it is the pump.  It could be that the battery is a bit low.  However, if it gets worse, then I would replace the old diaphragm with the new one from Moss.  The solid state pump should also have the latest type of diaphragm.