Here is a picture of the failed gasket from the hard start.
Other than the failed gasket, there were no problems with the motor. I made a new gasket and reassembled.
Today I tested out some modifications of the start sequencing. The results were good - 4 lights in a row on 5 tries with no hard starts. Unsurprisingly there is some art to getting a sequence which lights reliably without hard-starting. Moving the valve closer to the chamber gave better throttle response as well. I'm working on a post with details of my ignition system (you'll be disappointed). Unfortunately, I'll be out of town this week on business so this movie of today's run will have to do for now.