I took the old plugs and soaked them in some cleaning solution. This clean solvent was given to me by the airpark owner. he gave me a small amount of this. He told me it is used for cleaning aviation injectors and such. I soaked two of these plugs in about 1 inch of this. This is what came out of two of these plugs. After cleaning these plugs do not look that bad. If this was dual ignition I would reuse these. These will go up for sale on e-bay for 25 bucks each.