Help! Used wrong gas in lawnmower

Have inadvertently used oil/gas mix intended for the chain saw, in our 4 stroke Briggs/Stratton. No problems at all. I was surprised also that the posters engine would have 'stopped' running due to the use of 2 cycle fuel! Have seen somone put kerosene in one of those. Since the engine was warm it started up and ran fine for the remaining thirty minutes to finish a job before dark! I don't think it would have started cold though; BTW according to one B&S book I've seen there is (or was) a kerosene version (not diesel) of some of those those engines and also, apparently, one that ran in the opposite direction (i.e. backwards). Don't have the details in front of me but I assume they would have been versions of the horizontal shaft models; not the vertical shaft commonly used for lawnmowers? AFIK two stroke engines (including outboards?) are still sold in North America. The only advantage I believe is lighter weight for a certain power output? Versus increased pollution; viz medical effects, corrosion, air quality, damage to vegetation and structures etc. etc.
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