MG Car Repair: MG B Anti-run-on Leaking Gas, crankshaft bearings, carburetter

Question
Suddenly, as I was about to drive to the country in the evening air, it didn't want to.  I found a puddle of gas beneath my car and after troubleshooting, found it was gushing out of my anti-run on valve (bottom).  I've been trying to find out what would cause this, to no avail.  All the pictures in the manuals show a breather pipe coming off the bottom of the valve, I can't find mine anywhere.  The car won't start, seems gas doesn't get to the carburator (guess because it's all falling out the bottom of the anti-run on valve).  
Where do I start?  I had a match in hand, ready to drop it in the engine compartment (to see better) and common sense took over and told me to write somebody smart.
Help, please...
Wayne

Answer
Hi Wayne.  The anti run-on valve is attached to the inlet manifold.  When the engine is switched off the valve should open, flooding the inlet with AIR (not gasoline).  

You have a real problem here.  I think something has failed inside the carburetter so it floods the manifold with gasoline.  Do not run the engine like this.  The flooding carb may also cause fuel to get past the pistons into the sump.  This will thin the oil, and the engine will then destroy its crankshaft bearings.  Also, the crankcase could literally explode (I am not joking).  

If the dipstick shows HIGH, then you will need to drain the contaminated oil, change the oil filter, and replenish with fresh engine oil.  No point in doing that until you have found and fixed the problem.  

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I gather that you have HIF type SU carbs.  These have an O ring on the cold start enrichment shaft.  Modern fuel (with Ethanol) is not compatible with the material that these O rings were originally made from.  The O ring fails, and fuel then floods from the carburetter directly into the inlet manifold.  I advise you to buy two new O rings from Burlen Services of Salisbury UK.  They have re-manufactured them to be Ethanol tolerant.  Ask for part number AUD3602.  You require one O ring per carburetter.