I just jumped on the Ahab bandwagon. Today a clear demo hit my mail.
The first thing I did was to change the O-ring. No problems, greased, assembled.
Then I did an overkill flushing - I took it apart, cleaning every single part with dish soap/water solution and then clear water; then I washed the nib and feed with soapy water using a toothbrush - multiple times. The feed was literally full of ebonite pieces. As I said, I paid extra attention to the feed, cleaning the fins and the channels with a hard toothbrush.
Then I assembled the pen and flushed it with soapy water using the piston. Then flushed again with clear water, disassembled the whole thing, dried with paper towels AND let to dry completely.
The whole process until I left it alone took an hour or so.
I assembled the pen again when dry and inked with Herbin Vert Empire. So far, it railroads a lot when flexed. The ink can get to the tip alright, but the flow is too slow. I tried various feed positions, and now I have the 9-fins-visible configuration. Still problems with flow. Readjusted several times, no help.
I'm letting it settle overnight, and if nothing helps, I'm taking it apart again tomorrow to repeat the cleaning process, and possibly running the blunt side of an xacto knife through the feed to be sure there's nothing left there. Do you have any better ideas what to do with it when the flow won't be satisfactory?
Oh, one more thing - I noticed that the tip of the feed is a bit asymmetrical. I mean, the tip of the feed is not centered with the central "edge" that comes down from the end of the bottom channel to the tip. So when aligning the feed, I can either position the whole feed in line with the nib (and have the tip leaning on one side), or align the tip of the feed with the nib, having the whole feed twisted a bit. What's more important when adjusting, the position of the whole feed, or of the tip itself? I guess this irregularity is not that significant and is just a result of the feeds being handmade, but I want to be sure...