Originally Posted by 1967brutus

I am not sure, but I do think, that occasional misfire has other reasons, that might very well are affected by scavenging efficiency, but not caused by it.
As it is, this engine differs slightly from full size Wankels in that it has a separate recess for the glow plug, that is connected to the combustion chamber by a tiny hole. There is not, like in conventional glow engines, a 1/4"-32 threaded hole straight through to the burnroom. This is done to offer the apex-seals an as uninterrupted passage as mechanically possible. Under normal circumstances (meaning, the engine being used as a glow engine) the cavity of the glowplug that holds the filament, connects directly to the tiny passage between the plug recess.

However, when a sparkplug is used,the plug-recess becomes a kinda-sorta precombustion room, but this space is only "scavenged" by compression and the blow-out after ignition.
So a succesful ignition depends on there being an ignitable mixture in that precombustion room. I have the impression that a succesful ignition is more or less a matter of "luck" for lack of a better word.

I know that full size Wankels require special sparkplugs with recessed electrodes for exactly this reason, but there are no "Wankel sparkplugs" in this size.
In fact, for this project, I had to slightly modify a sparkplug, shortening the mass electrode otherwise it would close off the tiny passage between recess and combustion chamber, and I had to select plug washers for thickness to prevent the sparkplug bottoming out. I could not simply cut away the entire mass electrode, otherwise the spark would most likely jump to the metal of the engine and erode away the engine locally.
As it is, I can see the clean spot on the mass electrode, so at least I have reasons to believe that the spark is jumping at the correct place.