I recently installed a Hot-Spark electronic ignition and had my SUs rebuilt. I have spent far too many hours trying to adjust the SUs correctly, my main problem was adjusting the idle speed. At 1200 RPM the engine ran great at 600 or lower it ran crappy. Whenever I started working on the tuning I would always hook up the tach before starting the engine. Today I started the engine and then hooked up the tach and holy mackerel, as soon as I placed the red lead on the coil the engine would sputter and stall. I guessed at the RPMs and seem to have the idling under control now. So, I think I have a faulty tach, and I thought I would pass this experience along to save someone else from going crazy. If anyone thinks I have other issues to deal with,let me know.