Most CDI R/C ignition systems have a shielded spark plug wire/socket. The socket is solid stainless steel & the wire has a briaded S/S cover over the conductor/under the sheath isulator.

Similar in consruction, but different in application to a coaxial cable for your satilite/cable TV leads. 2 condutors, but in the case of the shielded sparkplug lead the outer conductor is a ground.

The braided sheath & spark plug cover ground to the engine via the sparkplug base & also to the ignition module case.

In fact, a good CDI EI system would eliminate your magneto/flywheel, be less prone to RF ineterfearance & save weight overall.