Well, this discussion got me started on an internet search. Appears the idea has been around for a long time, going back to the Model T days (but with a blowtorch). One of the more complete discussions in one of the car forums follows. And I thought I invented the propane torch trick.
"Here is how I clean sparkplugs. I know it is effective because it has worked time and time again on old motorcycles with marginal energy inductive ignitions.
A "fouled-out" sparkplug usually fails to light off the charge in the cylinder due to conductive carbon deposits that have formed on the center electrode's insulator. If the ignition system powering the sparkplug is inductive, rather low energy, AND the high-tension side is connected to the center electrode (no air gap like in a distributor), then plug fouling can be an issue due to conduction between the coil secondary and ground (through the conductive carbon fluff).
Simply roast the center electrode's insulator - no plug disassembly required, with the flame of a propane torch (NOT an oxy/acetylene torch!) until the carbon deposits burn away. Hold the sparkplug with needle-nosed pliers on the threaded end where the plug wire attaches. When the hot carbon begins to burn away, you'll see yellow/red flames and the center insulator will lighten. If the sparkplug is a very cold one like you'd find in a motorcycle engine, by the time you get the center electrode insulator hot enough to burn off the conductive carbon the threads will be glowing red and the plating may be discolored somewhat.
Allow to air cool for one hour on some non-combustible surface, like your driveway. Use no brushes or solvents except for cleaning up the threads if you had not done that before the torch roast. Check/regap plug, add anti-seize to the threads if you are so inclined and reinstall.
This has worked great for me - your results may vary.
Seth"
