Prusa i3 hephestos wall gaps

Hello,

I've somewhat recently started with 3d printing, I'm using what is mostly a prusa i3 hephestos (a model sold by bq) and I'm getting decent prints except for one flaw that I can't correct. It seems sometimes there are gaps on walls or surfaces, like the one in the picture:



I believe (but may be wrong) it happens after combing or retraction moves.
In this case it was always in that same spot of the print and the print had no travel moves at that point. That picture is of the place after making the infill, when cura starts the outer wall. The infill was quite poor as the wall on the model was very thin, it looked more like it was dripping a dot at intervals.
I've used the printer to print raspberry pi sleeves and they come out with these gaps:


I'm using Cura with:
0.2 height
0.8 shell thickness
0.8 bottom/top thickness
50mm/s speed
Retraction 1.6mm at 30mm/s
220º Temperature (what says on the filament roll i should use. The filament is also bq brand)
0.40 mm extruder nozzle (the standard from the bq unibody extruder.

All my searches have come up short, so I'm asking if anybody has seen this problem and suggestions on how to fix it.

Thank you!
(Also this is my first post in the forum and I'm sorry if it isn't in the right place)

Edited 1 time(s). Last edit at 07/08/2015 12:26PM by mackh.

I'm not so sure, from the second picture looks like too high acceleration

Pic of the Hephestos?