'74 2.0 L, Dual Dellorto DRLA-40 Carbs, Conventional Ignition

Rebuilt my Dellorto carbs a couple of weeks ago. Everything has been ship shape till today. When I start the car, the engine will surge to mid-high RPMs on its own for about two seconds and then settle down immediately to a normal idle. This occurs even if your foot is not on the gas pedal at startup. Any ideas as to what is suddenly causing this surge? Thanks in advance.

Ansbacher