I have 1990's B & S 12hp I/C QUIET MOWER ENGINE MDL286707 type 0420-01. The Brand of chassis is unknown (two) questions please

(1) the motor produces no spark. I have cleaned the flywheel magnet & coil core. The Coil and spark lead show continuity. Assume the single black lead from the coil's primary completes to ground in the normal RUN condition. Grounding that lead made no difference.
Since I see no other leads entering under the flywheel except those for the generator I assume there are no points. How is it timed? All other wiring & safety interconnects seem normal. I suspect the coil. AND:

(2) With the gear shift in neutral and the brake released I believe that I should be able to relocate the mower by pushing it. BUT only intermittanty is this possible.. the wheels are locked.(or still engaged to the differential/transmission), to move the item, one of the rear wheels must be lifted off the ground. I have examined the gear changing linkage. It positively dedents into the FWD/Neut/REV positions. This is a multispeed, step selectable, transmission, possibly a hydraulic concept. Though I cannot see any sign of fill/drain plugs

Your words of wisdom would be appreciated

The black wire is the KILL wire! Grounding it grounds the charge. Timing will not be an issue for no spark. When the magnets pass the magneto it will spark. Check to make sure the black wire is NOT grounded. If it is not, replace the magneto.

Hope this hleps,
Victor