I do a bunch of work with antique hit and miss engines. I will never again use a blast type cleaner on an antique plug! Champion 34s are a good example. They were originally made specifically for Maytag single cylinder 3/4hp engines. They are 1/2" npt, take apart, dual ground electrode, and no longer available. Years ago, I used a blast type cleaner on several. They ran fine for 15 to 30 minutes and quit firing. when I checked them, they were carbon tracked all the way down the center electrode to ground. On further examination, I found the center insulator to be "rough" from blasting. It had originally been very slick and smooth. I believe that blasting gave the ceramic a texture that made carbon tracking inevitable.
From then on, I clean plugs with carb cleaner and compressed air or a propane torch. Some of these old plugs get pretty pricey, and you do what works and drop what doesn't.
For my money, if I want a spare set of plugs for a car or truck, I'll just buy 'em.
Just my two cents worth.
Best wishes,
Les
