I was a problem with that but it solved by the thermal barrier. guaranteed
KesL, MK8 or MK7 types extruders always jamming for a few reasons.
First, yes you have jamming problem, so you don't extrude after 1 or 2 layers. Yes, your temperature is hot but hot temperature is not real cause.
Do you know what types of steel barrell using in your MK8 extruder? if your barrell don't have the thermal barrier, you will jamming even if you down to temperature. take to pieces your extruder and look to the your steel barrels. if there isn't thermal barrier(teflon), please change it to the new barrell with thermal barrier. and also add the heat sink to your bar mount chasis block, it is really helpful to create the heat circle.
Custom 3D Printer,
Mechanical Engineer