The plug has dry thin black deposit on it. No part store in town could match the number on plug up with a replacement! One place was able to match up the bore size, but all the ones with right bore size have the usual thick brass snap-on electrical connection. This one just has the thin threaded post. I suspect any plain old lawnmower-type plug would work. I can't think of some way to spin the engine up to actually test the spark with plug out and outer part grounded with a jumper clip to engine ground. (without having a dynamometer to put the rear wheel on that is). Thanks, Jim