[link=http://www.allstar.fiu.edu/aerojava/faq_princ_flight.htm#impulse]Read this FAQ on inpulse couplings.[/link]


The fact that you should replace a faulty ignition switch, or secure the ground wire when a ground run up reveals that the magneto will not go off is not the point. The point is that this is often intermitant and may not show up during a run up. For example a loose ground wire may vibrate enough to maintain enough contact during runup to cause the RPM to drop on one mag, yet be an open circuit when off failing to ground out the mag.