I am kind of stumped. Note I worked for many years as a mechanic and as an electrician. I don't say that to pretend I know everything. I mention it to indicate I am not totally clueless.
I am teaching a home-school group soon an intro course on engine mechanics (mostly small engines). 10 kids. I wanted to get some cheap diagnostic tools for each kid. $9 for each student and stuff direct from China $9 buys a digital multimeter and a spark-tester. The multimeters work fine. I tested them all with various voltage ad resistance settings. The spark-testers do not work and it is hard to believe. Not much there to go wrong. I have never owned a factory-made tester before. I always just made one from a piece of copper-core plug wire and an old spark plug with the ground-electrode removed. Those have always worked consistently well. With 10 kids coming, I figured it was easier and cheaper to just get these things from China. $3.50 each to my door. I have a 1936 outboard motor here I tried a tester out on. No spark to see. Tried my home-made tester and get a bright blue spark. Note the Chinese tester is adjusted with the same gap to jump. I then went to Autozone and spent $8 on one of their el-cheapo testers that looks much like these Chinese testers. It also shows a bright blue spark. How can this be? Note the Chinese tester has a long wire-lead instead of a ground-clamp. So I removed that wire and clamped the tester directly to engine-ground and it still does not work. I also checked resistance and continuity on all relevant parts and all checks fine. ??? I am almost to the point I am just going to buy 10 new D16 spark-plugs and just make 10 testers. But this seems to defy reason. Note I have also tested in a dark room and see no spark escaping anywhere. The Chinese testers DO work on a high-energy ignition source but not on most of the small engines I have with flywheel magnetos or self-contained magnetos. Battery-coil ignition - yes. I posted a photo of the Chinese tester.
I am teaching a home-school group soon an intro course on engine mechanics (mostly small engines). 10 kids. I wanted to get some cheap diagnostic tools for each kid. $9 for each student and stuff direct from China $9 buys a digital multimeter and a spark-tester. The multimeters work fine. I tested them all with various voltage ad resistance settings. The spark-testers do not work and it is hard to believe. Not much there to go wrong. I have never owned a factory-made tester before. I always just made one from a piece of copper-core plug wire and an old spark plug with the ground-electrode removed. Those have always worked consistently well. With 10 kids coming, I figured it was easier and cheaper to just get these things from China. $3.50 each to my door. I have a 1936 outboard motor here I tried a tester out on. No spark to see. Tried my home-made tester and get a bright blue spark. Note the Chinese tester is adjusted with the same gap to jump. I then went to Autozone and spent $8 on one of their el-cheapo testers that looks much like these Chinese testers. It also shows a bright blue spark. How can this be? Note the Chinese tester has a long wire-lead instead of a ground-clamp. So I removed that wire and clamped the tester directly to engine-ground and it still does not work. I also checked resistance and continuity on all relevant parts and all checks fine. ??? I am almost to the point I am just going to buy 10 new D16 spark-plugs and just make 10 testers. But this seems to defy reason. Note I have also tested in a dark room and see no spark escaping anywhere. The Chinese testers DO work on a high-energy ignition source but not on most of the small engines I have with flywheel magnetos or self-contained magnetos. Battery-coil ignition - yes. I posted a photo of the Chinese tester.