Do the tachs flutter back and forth when this happens? Almost like turning the key switch on and off very fast?

ya the tachs do flutter. drop maybe 300rpm then back up. o.k. for 3 seconds, rpm drop on other side , rpm back up, o.k. for a while , then drop!
but yes i will be there again tomorrow. to start recomission. i will check all fuel related links. and if i find water then dump carbs! think i will get this straighten out ! dam i hope so.

fuel problem, probably venting or air leak.

My first thought was what Gary said. Disconnect the synchronizer. You said it bounces back and forth from engine to engine. Sounds a little too controlled to me.
Too controlled for a water problem. Don't get me wrong though, check for water, but disconnecting the synchronizer is easy, and if it is the problem, the results will be immediate.

Paul