I have a custom 823 and Have been playing with different ink, and pen settings.
i Found the flex is best used when you
1. Pair the pen with a ink with less surface tension (most likely wet ink). You want to see the ink sticks inside the wall of your pen.
2. The pen railroad a lot less when it's completely filled than almost dry.
3. Open the filling knob in the back when you are writing. Having high ink level + filling knob open really helps to increase more flow to the nib and feed.
4. Use a oil shield. None of the set up matters if there are oil on paper... so use something to block your finger and hands from touching the paper, especially when you are using coated paper like Maruzen, Rhodia, or Clairefontain.
Edited by Innosint, 09 August 2017 - 15:50.