Not sure if this helps, but one plug fires twice within the 4 cycles --
once during the exhaust cycle, and once during the compression cycle.
One cycle = one RPM -- and, 4 cycles = 4 RPMs,
for tachs count each & every full rotation of the crank as one unit
One spark plug receives 2,000 impulses to fire at 4,000 RPMs.
Two spark plugs each receive 2,000 individual impulses to fire at 4,000 RPMs, so in the case of the 790, were talking a total engine / both plugs scenario of 4,000 impulses to fire the plugs at 4,000 RPMs.
I strongly believe that the firing ratio of 2 pulses per 4 RPMs per spark plug X 2 spark plugs remains constant throughout the entire engine operating range.
More about wasted spark, from the new King of Darkness -- Gill
http://www.gill.co.uk/products/digital_ignition/Introduction/8_wast_spark.asp
