My DCOE's had sat for years before I put them on my car, I had to pretty comprehensively disassemble and clean them before they worked even remotely well.

Various things I found in mine:

Some stuck accelerator pumps and return jets (which moderate the pump effect when the pedal is pushed in slowly)

Some plugged tiny holes in idle and main jets (very, VERY carefully clean these - if you scratch them up (with a little piece of wire, for example) you will throw off the metering. They have tiny holes and it doesn't take much to make a difference

Some plugged passageways in the carb body.