Chainsaw Repair

https://en.wikipedia.org/wiki/Four-stroking

Thanks for the link, I never thought there'd be a page on the topic!  There is some good info there that may answer my question and I will read it though more thoroughly later. 

There appear to be some things I'll disagree with too, including the statement "Four-stroking is not caused by an over-rich mixture".  Given that you can make it start or stop only by adjusting the mixture, the claim that it is not primarily a function of mixture is dubious at best.

Also, the claim that "Four-stroking begins gradually" does not match experience.  Four-stroking turns on and off like a switch with maybe a 10% change in rpm.

What appears on first quick read to be missing from the article is a good general understanding of how carbs work, and the fundamental difference between all position carbs and all other types - which just happens to create mixtures that get very rich with minor increases in air velocity.  Still, there may be enough clues to answer why it fires every other revolution, which is what I was curious about.