In a blender, combine bitter orange juice, garlic, salt and pepper, and puree until smooth. Place pork in a dish and pour marinade over. Cover and refrigerate for at least 2 hours or up to overnight.
Heat a grill to high. Drain pork from marinade and grill until cooked through, about 2 to 3 minutes per side. Serve with a side of Chiltomate, red onion salsa, a wedge of bitter orange or lime, tortillas and black bean puree.