My J1 kept jamming, both with IDEX (PLA with PETG support), but also with just a single PLA extruder.
Applying thermal compound (see other threads here) roughly cut the occurence in half but didn’t resolve it completely. Also applied thermal silicone to the top of the heat block as insulation, to no avail.
I then paid attention to when it happened and it was always when the flow was slow, such as:
- Overhangs, which default to 15 mm/s in Luban
- Top surfaces in situations where combing in combination with monotonic order would result in small extrusions followed by long travels.
Solution was to disable all combing and set overhangs to 50 mm/s. I would guess disabling monotonic order and avoiding ironing could help further.
Funny thing is that this resolved IDEX too, which I had always suspected was due to heat creep when idle.