inductor timing (points)

anyone no the gap for the inductor coil that took place of the points on a 1978 280z 4 speed trans. the car is jumping and jerking at 20 to 25 mph. runs great at high speed and starts good.changed plugs distrubtor cap roter button have changed vacumn hoses that were bad,same problem. if anybody can help please let me know what to do. thanks eric