Ended up getting a free nitro motor. It has great compression and had afterun oil or atleast wd40 used after the last time it was ran. This is the glow plug that came with it. Is it possible to tell if it was running rich or lean from the glow plug?
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There's some good discussion
here about that exact subject. To excerpt the most relevant bit, with my own opinions:
1 - good tune
2 - too lean, risking damage, flame outs, overheating, blowing plugs for performance
3 - slightly rich, acceptable for bashing and keeping an engine cool. Personally I would lean it out if the coil is getting that dark.
4 - overly rich
It's possible the plug you're holding now wasn't run for that long, an engine should go through several glow plugs over the course of its life. Glow plug "temperature" will also be a factor in whether the tune it develops is too rich or lean; a glow plug mismatched to the engine/fuel/weather conditions will be difficult to achieve a good tune with.
Basically, the richer the tune, the darker buildup on the glow plug will be. You want a "glazed" look, not completely bare, but not caked up with soot.
As an aside, cropping your pictures to just the glow plug would improve the readability of your post, as well as perhaps using macro mode on your phone to get clear images of the coil, it's not really visible in the pictures you've uploaded.
