Leaky carb doing my head in.

Glad to hear you got it solved. Maybe some holes for the carb throats to fit in. Have seen some use old rubber carb holders (between carb and head) to hold them.

Look at it this way, the bigger the PITA it is the longer you remember. You won’t ever do the same thing again  and neither will anybody else

Perhaps you could throw together something like this.

Excellent to hear David!! Nice Quote by Wookie! Although it was a "mystery", You worked thru it and won't soon forget it. Yes, regardless of carb type there's going to be a bowl vent somewhere. And if plugged will all exhibit the same behavior. Wish i would of seen that "holder" earlier, ha.  

 Butchered the carb rack to get the clearance needed for the bowl vents. All went well.Yesterday I got the levels sorted on No.1 & 2. Today I did 3 & 4. No leaks,fuel levels sorted,carbs ready to go back on the bike (weather permitting).
 Thanks again for everyones input and remember, if you build a rack to hold your carbs........!

Hey davido.
I attached some photos of my carb rack after some revisions.  I had copied a rack that Mikaw had made and added some more features.  The legs are set up so you can position the rack in any of 4 positions, holes for bench sync, access for jet and needle changes, remote fuel to set floats.  The tank is supported by a length of 1/2" pvc pipe in conduit clamps and the carbs are held with an old pair of manifolds.    

About the only thing it won't do is decide what jets to use!

Another photo, without carbs