This Waterman pen let too little ink flow. One day I put my finger on the upper side of the nib and pressed down against a hard surface a bit. It was just enough to spread the slit between the nib tines a little and the ink flows as it should now. Be careful when doing this, though, lest the space between the nib and the feeder increases too much. See step 8.
The Wahl Eversharp pen company once made a pen with an adjustable slot between the tines. This controlled the amount of ink available to flow onto the paper. In effect, it made one nib function as a medium or a fine point. See also step 6 for bringing the tines closer together.