BTW, in case any of you were wondering, that yellow splotch on the choke cover is not a paint daub/inspection mark, that is the residue from a piece of yellow plastic tape (like electrical tape) that got hot and fell off after the choke warmed up the first few times.

*Pacific, I think the plug you are asking about is a lead plug sometimes found in the end of the cast metal tube (in your pic your tube is threaded).