Q:

Why is my print getting messed up mid-print?

I am using Slic3r to generate the GCode for my Marlin-based printer. For some reason with increasing height my print starts to get messed up. On another part it starts to act like this when there are small parts. Is this related to my Slic3r settings, maybe to much filament being extruded or is this due to something else?
Any help is highly appreciated and I can provide more pictures of messed up parts or slic3r config if necessary.

A:

To me, this looks like a combination of bad filament, high temperature and/or fast speeds.

Too high extrusion temperature will make difficult to let each layer cool enough before the next layer begins. This is why you see the poor results on the smaller areas of the print in your second photo.
If you're using bad filament (out of round, non-virgin, or poorly stored filament) you might see a series of over/under extrusion areas or smoke from moisture in the filament.
Slowing down your feed rates can be tricky if your extrusion temps are too high. By slowing down, you're allowing layers to cool down a little bit more and solidify. If your previous layers are still relatively molten, you'll notice that the new layer of filament will adhere to it and potentially drag the previous layers as the nozzle continues to move. You'll see the results of this in the top-arc layers with an uneven curvature.

