Pen Gripes and Questions.

[HogwldFLTR]

I've noticed a habit of my fountain pens to halt and stutter the flow. It seems more pronounced on the Mountblancs I've got (but again I've been using them mainly). Is this common for fountain pens?

Also, I have a couple of cartridge pens and a couple of piston or converter loaders. The advantage of the non-cartridge pens is the ability to switch inks with less waste then on the cartridge ones. Has anyone experience in keeping cartridges which are partially full and using them again later or are they just lost if trying to switch inks?