38racing wrote:I ran it for a couple extended runs and then took it to him. Yesterday he told me that he cut the front lawn and half the back and then it stopped. He waited an hour and then finished the backyard. I know it sounds like a bad coil but I'm having problem understanding how a bad coil would have it slow to idle but not stop completely during my tests and fact inline tester showed a spark. And it would restart and either run slow or maybe even fast.
Ever thought of that you might have a failing spark plug that might shorting partially? A shorting plug will not show up using an inline tester nor would the inline tester show a timing issue.
Also with electronics involved just anything possible from reduced spark to timing issues. I had bad coil electronics that threw the ignition timing so far off that it literately sat the air filter on fire. Another other one wouldn't even fire the plug on compression but ignite the exhaust with a nice 12" flame. That one nearly sat my pants leg on fire. I even had one act like the governor was out of order oscillating the engine.
Of course if wasn't for me working with diesels I would have never thought of a 2 cycle dieseling because of a bad spark plug. I was kind lucky at the time to have an inductive tach connected when the rpm limiter kick in. The tach showed zero rpm yet the unit was running wildly at full throttle. It turned out to be a bad spark plug. Even the Stihl techs couldn't find that one, just said nothing was wrong with the hedger.
About the way to know for sure is to change the plug to a known good plug and test. If still does it then trying the coil with a known good coil and test. Then if the problem goes away then you know one of the two was the problem; otherwise, the hunt continues.
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