Idle kickdown

I have triple Webers on my 240. Runs great, but when I come to a stop, be it at a light, stop sign, etc.; the idle stays at about 1500 to 2000 rpm. If I give the gas pedal a sharp kick, the idle may or may not drop to the 800-1000 rpm range that I set it at in the garage. Sometimes takes two or three raps on the pedal. Linkage is free, also have some good return springs on the linkage. I have the Crane optical ignition in the dist., so there are no points. Not running any vacuum advance. Could the centrifugal advance be hanging or do I have wear in the distributor? Any ideas/theories would be appreciated.