I would check the sparkplug cables, then I would check the point. If they are fine, then check inside the distributor cap if the contacts are in good shape, then check if the rotor's contact is in good shape, and then check if there is any 'play' in the rotor, hold it, move it clockwise and anticlockwise, it should NOT move.. pull and push it, it SHOULD still not move.. if it does, it could be your problem..