Backfiring & Hard Starting When Hot
Maybe in left field. maybe not.
Old '74 XLCH 1000 (points & condenser ignition)- backfiring, with flames shooting a couple feet out the pipes indicated that the points had "slipped," point gap had closd up, and points plate had rotated . increasing advance (I think - it's been a long time since I converted to electronic ignition). Is this possible with electronic ignition? Dunno, but if the Hall effect or whatever trigger is used has "slipped," I think so.
Hard starting with electric starter on a '82 FXWG or '78 FXE (don't remember wihch, same starter system anyway) when hot, OK when cold - corrosion in the + cable to the starter solenoid, not on the terminal but within the cable itself. Finally noticed the cable was swelled, took it off and, inside the insulation the copper was gray-green and powdery. Bent thje cable back and forth a couple of times and it broke into. When hot, resistance in the cable increased and she wasn't getting enough juice to spin the starter. This is possible on anything.
Probably no help but maybe a direction in which to look.