<...he thinks there was a plug not firing until the engine started warming up ...>
All these problems with plugs getting flooded and engine won't start.  I've been wondering if anyone uses starting fluid.  When I was in the auto repair business I used it EXTENSIVELY to clear floods and also as a "primer" after a carb rebuild to keep the engine running while the fuel pump filled the float bowl.  Wonderful stuff.  Lots of wives' tales about tearing up engines.  Get past that and it's great (particularly for clearing floods - combustion always seemed to consume the fuel around the electrodes and insulator.
Wonderin' if it works on rotaries - or if anyone has tried ... Jim S.