Help with Sheaffer Snorkel Skipping?

[tudor]

Some of my family members gave me a Sheaffer Statesmen Snorkel that they found while preparing for an estate sale. I cleaned it out several times with water, but I never saw any ink come out. Maybe it had never been inked? Anyway, I filled it up with Monteverde Yosemite Green, and it initially - for a page or two of an A5 Clairefontaine journal - wrote like a dream. Then the pen started skipping. Just a bit at first, but then it was every other word or so. So I emptied it out and re-cleaned it. And then refilled it with Pilot Iroshizuku Tsuki-yo. This time I got about 3-4 pages and the skipping started again. I got rather frustrated and left the pen inked up in its case for two days. I picked it up, wrote a page beautifully, but then the skipping came back -- with a vengeance. (See the picture).

I've never had a vintage pen before. Is there something I'm doing wrong? How do I even prime the feed on the Snorkel? Does it even have an ink window? Surely it wouldn't have run out of ink already? Are there adjustments I can make? Thanks!