How can I make my black beans less dry?
What I would suggest is rather than adding a syrup, to take some of your cooked beans, cook them a bit more, then liquify them in a blender. This should give you a thick sauce that tastes like the beans, therefore compliments them perfectly. You can then thicken them very slightly if the consistency is still too runny, be sparing with the flour though. 

In fact, you could probably make something satisfactory by simply using less thickener. If you have a pasty, sticky sauce it's a classic symptom of too much thickener. Try making a roux with some butter and flour, cook it awhile for a dark roux which gives deeper color and more flavor. You can then add the roux in small amounts to your cooking liquid until you get the right consistency. 

If you are pressed for time and have some available a couple big spoons of refried beans may just do the trick too.