I figure OS means that once the engine is running, that if the rpm (calculated from the pickup pulse frequency) drops below X rpm then the cdi will automatically cut so as to prevent that one last backfire before stopping or kicking back into reverse opersation.

Unless it's actually measuring the pulse width as well then there's absolutely no way the cdi knows how fast you're cranking it for a single flick with 2-3 seconds between pulses so I'd expect the "minimum rpm" function to be disabled because I doubt too many people flick the prop over 3-4 times per second giving the cdi enough pulses to calculate an rpm.

MTK, could you please run a little test for me to put to bed my understanding/misunderstanding of this whole "minimum rpm" thing? If you get the time could pop a spare plug into the plug cap, turn the motor over by hand at a constant rpm 30-60 rpm and let me know if it sparks each time.

Cheers
Brett