Unless someone has bypassed it, your '84 has an ECM that controls the fuel and spark (timing) delivery to your engine. If you have advanced the timing more than what the ECM can handle, this may explain why you're now having problems. I would suggest returning the timing back to within a degree or two of what the factory specified, 6*BTDC w/either the 4-wire connector(carbureted 350) or the tan/black bypass connector(fuel injected 350) disconnected. You may also need to reset your base idle speed and clear any trouble codes store in the ECM.
Robert Yates for President!!