I have a 54 235 that is failing to start or keep running at times. It was doing fine then decided to quit I checked and no fire to plugs. so I went whole hog and replaced coil, condenser, points,rotor and distributor cap. Fired right up let it run about 20 minutes shut it off and it wouldn't restart. Checked every thing again it fired up. cut it off it wouldn't restart this time I checked the coil by pulling wire from cap and putting it near ground plenty of fire. put a test lead on - side of coil fire when points move consistent. took spark plug wire to groung no fire. Rechecked coil fire plenty again. checked spark plug wire none. checked distributor cap seat seems to be in place correctly. Why would the rotor not transfer spark to cap and wires part of the time and be fine part of the time?