Lay the carbs on a table, throttle plates (butterflies) up.
Stick a flat blade screwdriver in the throttle linkage to hold it open a tad.
Straighten out a small paperclip.
Use the idle speed adjuster to set the throttle butterflies so the paperclip just fits between the throttle plates and the carb body on the downhill side.
Adjust the screw between the carbs using the paperclip as a feeler gauge to get the throttle plates exactly the same.
I know, it sounds jackass as hell, BUT if you follow this procedure the motor will pull even vacuum on both jugs at 2300-2500 RPM someplace... which means at cruising speed the mirrors are still and clear. Vacuum (on my Morgan Carb Tune) will be even at 3 places, one at as much RPM as the idle adjuster will give ya, one at like 2400, and one closer to idle. Believe it or not I can static sync and the hook up the Morgan and the damned thing is dead on.