Ty, I'll have to get my spare mower out of storage under the house to take pictures of its Minion carburetor. Meanwhile here's some technical detail:
http://www.tpub.com/content/recoveryvehicles/TM-5-4240-501-14P/css/TM-5-4240-501-14P_105.htm

I'm still not clear on that coil in sparker's mower, it looks like a pre-Magnatron one, but it can't be because it would require the base engine to have points.

My current suspicion is that sparker's engine had a home-made governor link that simply refused to pivot at the butterfly end, and jammed the linkage.