I have an Anycubic i3 mega-s printer which Ive upgraded to an E3D V6 all metal hot end because of the high temperatures involved in printing PETG and all the good things Ive heard from it. But I could never get it to print CF PETG properly with it. I can print CF PLA or regular PETG filament just fine, but when I try to print CF PETG, I always get the click of death. Its not because the nozzle is too close or anything, it just happens halfway through a print. What I figured the problem is the filament melts into a blob inside the hot end, when it retracts and gets pushed through the nozzle again it jams on SOMETHING and it doesnt extrude anymore. If you back the filament all the way out and reinserts back in, it will start extruding again. Ive tried a number of things to solve this issue. Ive tried slowing or speeding up the print. I tried printing cool or hotter. Ive tried increasing the retract distance to 10 15mm, but none of those things seem to do the trick. The only way to stop the jam from happening is not have any retraction at all. I was able to carry on a 10 hour print fine, but the quality was HORRIBLE to say the least. Stringing everywhere, over extrusion, horrible surface quality etc.

Some would say then dont use CF, it doesnt help with the strength of the part, which they are absolutely right, but theres no other filament available which I am aware of that has the same carbon color and the matted texture as CF filament.