Mk2 print failures with  

Mk2 print failures with

I am trying to print the corvid mask with Prusament PETG Prusa Galaxy Black on my i3 Mk2. The printer has worked doggedly since I built it in 2015 and upgraded to 1.75mm a year later. I have previously used PLA, ABS and Carbon fibre for projects with great success. Being stuck in lock down with no immune system I decided that part of my escape plan would be a more effective mask than a bandanna. 

I ordered a Mk3 for which I am still waiting and I've been trying to print eh mask on my Mk2.

After a lot of tweaking and back to basics kind of adjustments I am getting great calibration patterns and the batman I printed is in my hall of fame ofr being almost perfect. I thought I was ready to go for it with the corvid mask ( https://www.thingiverse.com/make:786266 ) 

My challenges with getting the batman to work were nozzle blockages and the extruder slipping. After carefully adjusting the extruder spring tightness I had some success. The first mask printed for 498 minutes (I had the layer hight way too smal and it was going to take a long, long time, but I got 7 mm height. The first layer was perfect and until it stopped feeding it was a great print. 

I changed the first layer temp from 240 to 250 and the subsequent layers from 250 to 255 and got as far as 30mm, or more importantly 60 minutes of printing and then the jam. I changed the layer height according to the instructions so the extra height is a result of that, I can still only print for an hour. My best print so far is attached. When I stop the print, I can back of the filament with the extruder and then advance it past the blockage so it's a strange kind of failure that I have never encountered before. 

The second image is the filament that I pulled out (unload filament brought it right out with no fuss.). As you can see there's a thickening at the end where it was being compressed and on the left you can make out the tool marks where the extruder gear was slipping. Like I said, I could back this off and advance it when I had stopped the print so I have no explanation. 

Any suggestions most welcome. I am current experimenting with even higher temperatures to reduce the pressure at the nozzle.