That seems to have been it. It started right up today and though it died the first time I went to full throttle on the ground, thereafter it seemed just fine. I shut it down and restarted several times and it always ran without any indications of the prior problem. No smoke after I shut down and the engine cooled off normally after a run.

I did two short flights and had no problems with the engine.

So now I need to check out the Puppeteer.