This seems a retraction problem what can i do to fix it?
Top? Bottom? Side? of your print? A link to the STL file somewhere? Were you going for a groove in the side or was that unintentional? Is the dark spec a hole or piece of debris in the plastic?
Need more details
It happens every time, for every model. It is where layer is finished and next layer starts.
Oh, so that is the side? Slic3r has an option to randomize layer start position to avoid artifacts like that.
You may also want to change your retraction setup.
In which way? More mm? Less? I’m using slic3r…
I would try lovering “extra lenght on restart”, maybe a bit less “Lenght” and also I would check if my extruder generally doesn’t feed too much plastic - to do so you can change your plastic diameter in Slic3r, or you can try some setups manually with gcode commands, read about M92 E .
Before trying “extra length on restart” try a lower retraction speed and maybe a longer retraction distance.
I had to lower my retraction speeds to 30mm/sec on some greg extruder 3mm printers. 1mm retraction seems fine with a direct extruder, but you may need 3-4 with a bowden extruder on your delta.