Evenrude 50 hp run away engine

[touche]

I have a 83 50 hp evenrude mod e50belcrm that will over speed or run away .it will increase in speed and with throttle in nutral, it will continue to run with key off and battery disconected it will run at high speed for about 60-90 seconds after batt is disconected.is there anyway to fix this problem thanks touche