A rod runs from the accelerator pedal to the intake manifold venturi. Connected to this rod is another rod which connects to the rear of the pump (pneumatic vacuum governor. Try to shorten this linkage (rod connected to governor) up to such point the the engine doesn't die upon decelleration. Or, unhook the rod opposite the governor, and pull it up a bit while accelerating and decellrating. If it cures the problem, shorten it as needed.
This rod is supposed to mechanically assist the governor to stay at idle and not die during sudden decelleration.
I hope this helps.