What may be missing here is that just because a plug will glow with the battery connected, doesn't mean it's OK. In addition to a minimum heat, first supplied by a battery and then by the heat of combustion, there is the catalytic reaction between the materials making up the element of the plug and our hydrocarbon fuels. If the plug has been in service for a while and or become coated with... something... this catalytic reaction will not happen properly and the engine will not run (well). If the plug glows brightly but the element is either coated with carbon, silicone or the catalytic elements of the plug have been abraded, the plug is still not going to work (well). Plugs have a finite service life even if they don't physically fail.

As a side note, often "blowing" a plug in flight does not necessarily mean a dead stick landing. If the element is still in place and simply broken, the first sign of trouble we be when you go to start it on the next flight.

I'll stick with my recommendation in post #2.... Try a new OS #8 and fresh fuel and THEN begin troubleshooting. I'll add the followup recommendations of, ditch the extension and castor.

Bill