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Have you checked the position of the lever where the throttle cable goes onto the injector pump?
So the injector pump is set to idle when the engine goes WOT or does it all happen so fast that you haven't been able to check before turning it off? You would expect that either the injector pump is going WOT throttle, the pump is faulty and starting to badly overfuel, or the engine is starting to go into runaway. I haven't come across this before. I assume that the throttle is at idle when the engine is previously shut down and not advanced at all prior to restarting? No one (kids etc) could be playing with the throttle between trips?