It's been mentioned on this list before but I think the procedure for installing the K-cup is very important. For various reasons K-cups often have pressure built up inside. When the top of the K-cup is pierced, when lowering the lid, the pressure blows unbrewed coffee into the upper needles which can cause a clog. I think it's better to first use your two thumbs to press the K-cup firmly down into the cavity which pierces the bottom and relieves the pressure . That way coffee grounds won't blow up into the upper needles when the head is lowered. As always, good luck and your mileage may vary.

I had trouble with the Keurig brewing short cups. It would lose its prime. I found that the model I was using had a very tight fitting lid on the water reservoir. When the Keurig tried to pump water from the reservoir a vacuum was created. The water leaving the reservoir needs to be replaced with something ... and that would be air. The pump was just not able to overcome the vacuum. It worked perfectly with the water reservoir cover removed. I wanted to use the cover so I simply drilled a small 1/8 inch hole in the cover near the back of the reservoir. This is all it took. The air coming through the hole is enough to prevent the vacuum from forming. It's been going strong for over a year.