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   Post on Strange Tach Readings in Two Strokes

   By Gerry Visel, posted 4 Aug 2021

      I was resurrecting an Avid Mark IV with a 582 that had sat for five years.  After overhauling the engine, I reinstalled it, and hooked up the tach to the normal tach wire from the engine.  When I started it up, I was getting tach readings only on one side.  When the switch was in the Left position, the rpm sagged a bit as expected, but the rpm reading dropped to zero.  After weeks of asking around and troubleshooting (and fixing other issues!) I finally asked Brett Lawton from Leading Edge Airfoils (LEAF,) who had the answer!  
   Although I cannot tell you exactly why, this issue is not uncommon when using an electronic monitor like a Dynon or EIS. To remedy the issue, use one of the lighting coils wires for the tach signal and the issue should be alleviated.
      Sure enough, the Taskem Model J tach had been connected to the brown tach wire coming from the engine. I disconnected it from there and connected it to one of the yellow wires going to the regulator, and now it reads correctly in all switch positions!  YESSS!!!  The prior owner must have only been getting readings on one side and thought that was normal.