I'm pulling 20Hg of vacuum at idle.
This may be the key.
My guess is that you have the idle mixture control screws too far out and thus a VERY RICH idle. This creates "puddling" in the intake. When you open the throttle, the sudden burst of air into the cylinders sweeps all of the puddles into the engine, creating an instantaneous overrich condition rather than lean. The mixture is too rich to fire, thus the hesitation. Try readjusting the idle mixture. No more than 1 turn on each mixture screw. Set the idle RPM with the positioner screw.
Jon.
