Those zits are telltale of pausing with no control of back pressure. Just too much for the little Mr coffee processor to handle.
I just built a delta with a beaglebone black, a CRAMPS cape and running Machinekit.
Dessicants (more), heat goes up and downs while printing (is the window opens?) I’d say oozing but there’s no stringing, speed up the print (works wonders)
Okay, mostly solved:
The problem was too much overlap + too much temp.
The plastic extruded while infilling was pushing the perimeters a bit, so on next layer the plastic pushed use to extend along all the deformation, so along 2 or 3 layers, this deformation was extended. It also appears on spiked corners, because of jerk.