My bike calls for a plug change at every 7,500 miles. You're close enough. And you broke the diamond cutting carbon build to that white powder also; which can chemically weld the threads with the electrolysis between different metals. Keeping them in too long is a no-no. You were wise to pull early. Can't separate Mag from E, from chemRE, right? Look at the left plug. See how round the corner is on the side electrode? E wants to find the shortest path, so it wants a sharp corner, not go round and round looking to jump.
Nose inspection is one fast way to see if it's wet/black/white/tan. But you'll need a special tool by champion plugs, and you use that flashlight with magnifier to look down into the plug to read the ring base of the porcelain. Surface talk is about all you can do, not how well it's tuned.
Side Electrode:
Left is being eaten so change both even if the other took the better beating, it still loses material on each spark is the arc weld.
Burned tan carbon build. E can pass over and in a surface so the cleaner metal is a path that won't jump and misfire.
Porcelain Tip:
Front plug is dry, not covered in black soot, nor is it lean white, and is not shinny wet with oil. That's all I read nose wise.
Rear plug is as equal in nose colors, but say, rear might be lean from a few degrees of heat, not a cooler shot of the front say. I need to shoot a temp gun at a runner to see if that other color is caused by the air blocking, sans a comp test or leak is much better to see who is low.
Plug Gap:
Factory: You'd think they'd have it right with all the testing of engines, but what do I know, I leave it alone.
Wide from fac says, the gap might be too far to jump, so if wide is the gap, think throwing rocks all at once at a building and those windows stacked in that 15 story high building. Say you knocked out 12.
Narrow gap from fac say, throw the same rocks and you lit off how many molecules are the windows broken in that gap?
