Thin sections fail

I've been having issues with skinny sections of my print either being brittle, or breaking off completely. The rest of the print looks quite nice, but anytime there is a skinny section, I'm holding my breath. Anyone have any thoughts? I have a makerfarm Prusa I3. I'm using cura to slice my print. I've got a .5 mm J-head and this print is done with ABS. Print speed was 40 mm/s, temp 220 degrees. Retraction speed was 40 mm/s with a distance of 2mm. If you need any other info, let me know. The part I'm printing was rather large, so I wouldn't think it should be a cooling issue.

Thanks in advance!

At a guess I'd say that's a retraction issue. It's as if the nozzle retracts ok but doesn't prime. On thick sections you won't notice since the dodgy permiter is hidden. On thin sections it isn't priming after the retract causing a lack of material.

Likely cause is skipped steps in the extruder.

Try printing with a lowered retraction speed (say 10mm/s for starters) and lower extruder acceleration and jerk. You can work speeds/accel upwards from there. (on the fly if you use marlin)

If this doesn't improve things, try disabling retraction for a print.

I find a geared extruder skips steps on the prime at above 25mm/s retraction.

Also 2mm seems like a lot - I would be surprised if you needed much more than 1mm on a non Bowden setup. Perhaps skipped extruder steps have caused you to set such a high value.

I've got direct drive and 3.2mm at 70mm/s sometimes isn't enough.

Of course I've got the notorious, original Solidoodle 3

I appreciate the comments. I'm in the process of trying different retraction settings. I did a quick test print with no retraction. The piece seemed solid, but obviously there was a lot of stringing. I'm going to slowly increase retraction from there to see if I can find a happy medium. My current firmware settings are as follows:

#define DEFAULT_MAX_ACCELERATION {1000,1000,5,1000}
#define DEFAULT_MAX_FEEDRATE {250, 250, 2, 22}
#define DEFAULT_EJERK 5.0

Any thoughts on those?

Thanks!