TOPIC:

just looking at your photo.
which chain was sparking and where was it sparking?
Do the wires marked in green have enough distance from the final drive chain?

You may want to check and make sure ALL your ground wires are in good shape.

Rick H.

OGC,
Rick maybe onto something.
Take your meter DC V.
black probe on negative terminal
red probe on starter case.
you should have zero volts
Anything above .5 V shows a bad ground

You pulling 12V at the starter bolt pointed to this.
Double check your main ground to frame from the battery.

You want to put the black probe on the negative battery post
and probe different points with the red probe to verify the engine case and frame have good grounding.
You should have below .5 V at all points.