I finally received the carburetor kit. I completely rebuilt the carburetor including removing the Welch plugs and clearing all the ports with a small wire and carburetor cleaner. I replaced the emulsion tube o-rings. I replaced the primer bulb. I found a very helpful document on-line about servicing my particular Tecumseh carburetor (series 11). I found that the tiny port in the tip of the idle restrictor screw was completely plugged. It was difficult to get it open but I finally succeeded with a very small needle and a piece of small gauge wire that I cut off of a wire brush. Even the small wire in a twist tie would not fit through it (is this normal?). I assume that this blockage was most likely the cause of the surging.
The mower started easily and the surging was gone!! However, it was missing occasionally. I had replaced the original Champion RJ19LM with a new, equivalent Briggs and Stratton plug. I removed that plug and measured the resistance. It was 11,500 ohms. Too high? Should I be worried that my coil\ electronic ignition is weak? I tried a non-resistor plug that I had in my old parts box (Champion J19LM) and the engine ran perfectly! Since this is a model with electronic ignition, I assume that I should use a resistor plug. I am going to find a non-Champion resistor plug (is NGK-BR2LM OK?) and try it.
Anyway, it runs fine now. Thanks to Rivets, slomo and Tinker Ty for the great advice.