I believe I may have made a mistake, I purchased several packages of Pelikan ink cartridges, loaded one in my pen, and with in three days, my pen quit writing, I removed the front section and cleaned it in warm water, replaced it with the cartridge that come with the daycom kits,, I realize these nibs aren't the best, but until I put in the Pelikan cartridge it wrote reasonably nice,, I removed the cartridge, and noticed there was a more viscous liquid up at the top.
I replaced the cartridge with another Pelikan that didn't seem to have the same condition and it's writing fair, flow seems inconsistent, cleaned the nib and front section put the cheap ink back and it flow well and smooth, I suspect some irregtularity because I also bought 20 Gel refills all parkers, and have had to replace two out of the first five I sold, Will ink gum up in cartridges? I guess this is where I start learning to tune nibs!!

Please provide more detail, and others will contribute.

For example,

1. What pen are you using?

2. Is the pen brand new? If so, you might want to flush it with soapy water and then rinse. Manufacturing oils might be present in the nib and feed.

3. Were the cartridges made by Cross, containing Pelikan ink? Or are there cartridges for Pelikans....?

4. Were the cartridges of recent manufacture? Plastic is permeable by air; sometimes the air evaporates, leaving thickened ink.

5. Etc.

This probably doesn't apply, but one time (once in more than 20 years of using fountain pens), I noticed that a pen that usually wrote with a consistent flow suddenly didn't. It was a puzzle until I looked more closely at the pointy end that gets inserted into the cartridge. A tiny piece of cartridge was stuck in it, blocking the ink. It was hard to see and certainly a fluke...

My long-time friend Yuko in Nagoya, Japan, made a very bad mistake with her Mountblanc Solitare that she received after graduating from college in 1991. Apparently, she used very hot water to flush her pen out, which must have damaged the feed system. Sadly, it will no longer write, so I suggested that she send the pen in for repair. However, I don't think she has sent it away yet. Nonetheless, it taught her a very valuable lesson about not using hot water to flush out fountain pens.