keurig classic only brews a tiny bit of coffee then stops, like a partial cup. why?

The most likely cause is a clog in the exit needle.

Fix:

1. Unplug the brewer.
2. Press the 'PRESS TO OPEN' button, grasp the top of the K-Cup Holder, and push up from underneath to remove the assembly.
3. Remove the funnel by pulling on it.
4. Insert a paper clip into the exit needle at the bottom of the K-Cup Holder to loosen and push out any coffee ground clog.
5. Rinse the K-Cup Holder under a faucet. The holder and funnel are dishwasher safe.
6. Reassemble the funnel and holder, and snap the assembly back into the brewer.

If that didn't work:

• Descale the brewer. Mineral scale can hinder performance. You'll need 8 oz of undiluted white vinegar and a 10 oz ceramic cup.

Heads up: The entrance needle above the K-Cup Holder does not require cleaning. Do not put your fingers in the K-Cup chamber.