#7 could be just a wierd looking deposit, if not, then a chunk is missing all right.
Over all it appears ALL the plugs are burning cold for the fuel/ratio/timing you got. Advance the timing, lean out the carb or go one step hotter on the plugs is a thought.
#4 may not represent an "
oil" problem as much as a mis-fire for so long it accumulated
oil deposits. The plugs appear to be fairly new as the center electrode is showing minimal wear. The carbon build up would indicate to much "putt putting around". Watch the tack and keep the rpms up above 2K or better after the engine warms up. You "lugging" that motor?
As there is potential for loose carbon in the combustion chamber don't go out and "hammer" it. That will break loose the deposits and they will stick to the plugs. But DO get that rpm up, steady and get the engine HOT. Bring it home and SHUT IT DOWN right away, don't "putt putt" back to the garage.
Plug readings are best when the engine is immediatly shut down following a decent "run" at speed and temp. Temp needs to come up and STAY there about 20 to 30 minutes AFTER it reaches "normal" to get a decent "reading" on the plugs.
,,,,not that I know squat about plugs, but I did stay in a Holiday Inn recently.....
Ernie