The pics are quite shady and show little detail. From what I can see the plugs look sooty, as for too rich mixture.
I think you need to improve the light so it shines down into the plug. Also angle the camera to look down into the plug. 30 degrees off the plug centerline is about right.
Sunlight at high noon is best, but LED torches also are well suited.
Bulb light is no good for photographs