28-11-2020, 09:54 PM
Oil tends to give a shinier black look, its hard to tell from a photo. You seem to have what's described as dry carbon deposits. This could be over-rich mixture, but one would expect that to affect all of the plugs. An occasional misfire on that cylinder is another possibility, so check distributor cap, plug lead and plug gap.
It's sometimes the case that plugs soot up from rich mixture at idle. Ideally this gets burnt off by sustained running to get the plug tips hot enough, not always easy with a Seven. Some advise a plug reading technique which involves cutting the ignition when running and coasting to a stop to avoid an idling phase, but you need a quiet road !
It's sometimes the case that plugs soot up from rich mixture at idle. Ideally this gets burnt off by sustained running to get the plug tips hot enough, not always easy with a Seven. Some advise a plug reading technique which involves cutting the ignition when running and coasting to a stop to avoid an idling phase, but you need a quiet road !