The metal shielding keeps the RF from the radio.
Magneto ignition systems on Quadras and Zenoah and ALL convert6ed chainsaw engines have no shielding, just solid copper center coil wires and resistor spark plugs..
Non resistor spark plugs make major RF interference on these engines, changing to a resistor plug stops it....
Must be magic or voodoo...
Sometimes a Bosch cap stops interfenence on magneto engines, it has a 1K resistor in it...
Early RC EXL igitions had no resistor in the cap, just a short piece of wire like a paper clip plugged into the plug wire to contact the spring in the top of the silicone boot inside the metal cap...Have some here....They worked very well, still do, didn't have the funny advance curve....