Rans, further to my post in the Private Flying forum, this might be of use:
The magneto safety check is conducted with the propeller in the high rpm (low pitch) position at approximately 1000 rpm. Move the ignition switch from 'Both' to 'Right' and return to 'Both'; from 'Both' to 'Left' and return to 'Both'; from 'Both' to 'Off' momentarily and return to 'Both'.
When switching from 'Both' to a single magneto position, a slight but noticeable drop in rpm should occur. This indicates that the opposite magneto has been properly grounded out. Complete cutting out of the engine when switching from 'Both' to 'Off' indicates that both magnetos are grounded properly. Failure to obtain any drop while in the single magneto position, or failure of the engine to cut out while switching to 'Off' indicates that one or both ground connections are not secured.
Source: EA-AC 65-12A Airframe & Powerplant Mechanics Powerplant Handbook.
( Note - this is purely a safety check and not an engine run-up mag drop procedure.)
Steve.
Last edited by stevef; 22nd September 2008 at 05:06.