<VV> Carburetor mystery--Update

[Brian]

First of all I want to thank everyone who gave comments and advice the best I have ever seen to a question posted on the net.  I took every one of the suggestions very seriously and followed up on them.  Here is what I have found so far in no particular order.

Idle circuit-- every passage on the idle circuit was scrupulously clean I found absolutely no restrictions.

Venturi cluster-- all the Venturi clusters are also scrupulously cleaned and again no restrictions.

Idle siphon tube-- the idle cluster siphon tubes were also cleaned and again no restrictions.

Adding gas== it was suggested to pour gas in while the engine was running and see if it had any effect.  Was very difficult to do because the engine dies so quickly but I did try by adding gas and spraying starter fluid.  No effect the engine still dies very quickly regardless of throttle position.

Old gas-- this problem was replicated while the engine was on my run stand which has its own fuel tank to which I recently added fresh fuel.  So I sincerely doubt that old gas is an issue here.

Carburetor base== one of the comments said that I should check the base of each carburetor to be sure they were flat I did and they are perfectly flat.

Carburetor insulator and gaskets== I am using paper gaskets on both the top and bottom of the insulators.  The insulators and paper gaskets have been opened up to match the size of the carburetor.

Throttle plate-- another comment suggested being sure the throttle plates are completely sealing the carburetor.  I checked and they are and there is no leaks from the throttle shaft on the base of the carburetor.  As a precaution many years ago I added the rubber O-ring kit on all the throttle shafts.

Vacuum gauge-- it was impossible to get any kind of reading on a vacuum gauge because the engine dies so quickly.

Bottom line to all this I am still absolutely baffled.  I'm very thankful for everyone who is weighed in on this problem.  I'm hoping against hope that it will be some simple thing.  The fact that these carburetors worked for years and then suddenly didn't work with absolutely nothing being done to them is completely baffling.  Again many thanks to all.