sudden fast idle

[jfhilbish]

I have dual Cadron Solex carburators on a T3 motor. Just as the motor starts to warm up I get a sudden fast idle that doesn't go away after driving and makes shifting almost impossible. Some times the idle will drop on its own and sometimes slipping the clutch will cause the idle to drop. I have the back seat removed and can see the linkage to the carbs while this is happening. The linkage will return to the stops and the gas pedal has returned appropriately for my foot being off the gas pedal but the fast idle continues. Is this a problem the butterflies, an air leak or what?