Preheat grill for high heat. In a small bowl, mix together brown sugar, honey, liquid smoke and vinegar. Brush one side of the salmon with the basting sauce. Place the salmon on the grill, basted side down. After about 7 min., generously baste the top and turn fish over. Cook for about 8 more min., then brush on more basting sauce, turn, and cook for 2 min. Don’t overcook the salmon as it will lose its juices and flavour if cooked too long.