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I have 5 new-in-box Tempest UREM37BY spark plugs. They are still in the sealed tubes with copper gaskets. I purchased these from A/C Spruce over the past year or two so I'd have spares during my trips and at annual. No fouling with the extended massive electrode.
A/C Spruce sells them for $33.55 each and they have no stock. See them here at Spruce: Tempest UREM37BY Plug
The application guide is included in the above link so you can check if it will work for your engine. The smaller continentals use them as to the GO-300. I used these in my O-300 and never had a problem with lead buildup. They are also perfect for your O-200.
Price: $30 ea. plus actual cost of shipping in lower 48.
A/C Spruce sells them for $33.55 each and they have no stock. See them here at Spruce: Tempest UREM37BY Plug
The application guide is included in the above link so you can check if it will work for your engine. The smaller continentals use them as to the GO-300. I used these in my O-300 and never had a problem with lead buildup. They are also perfect for your O-200.
Price: $30 ea. plus actual cost of shipping in lower 48.