Explanations:
The engine makes two revolutions for each power stroke. To make 200 power strokes per minute, the engine must turn at 200 * 2 = 400 RPM. The starter motor must turn the engine at twice this speed, or 400 * 2 = 800 RPM. With a 2:1 reduction from starter to flywheel, this translates to 800 / 2 = 400 average starter revolutions per minute.
