MG Car Repair: 74 MGB SU carbs, fuel pools, seat valves

Question
hi Barrie - still trouble starting my 1974 1\2 MG. When I turn on the key,  the pump primes, but even before I crank the starter, both my SU HS4 carbs are flooding - the rear more than front. Fuel pools and then pours from the inlets. Choke is not engaged. I get no hint of combustion. My carbs were just fully reconditioned. The floats are ok and the needle and seat valves new and not sticking as far as I can see. I have good compression, spark etc.. the fuel pump is an SU. What are possible causes of flooding? I am totally perplexed.         
PW

Answer
Hi Paul.  You have HIF4 carbs.  They have an O-ring seal on the choke spindle.  If the O ring fails, the carb will flood internally, with fuel pouring from the inlet.  Sounds like whoever reconditioned your carbs failed to replace the O rings - both of them.  See part number 52 in this diagram:

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28997#52

Regards, Barrie