1/3 cup soy sauce
1/3 cup maple syrup
4 salmon fillets (about 8 ounces each), each about 1 1/2 inches at thickest part
Ground black pepper
Vegetable oil for grill grate
Lemon wedges for serving
For the Maple-Soy Glaze:
2 tablespoons soy sauce
1/4 cup maple syrup
Stir together soy sauce and maple syrup in small saucepan; bring to simmer over medium-high heat and cook until slightly thickened, 3 to 4 minutes. Measure 2 tablespoons glaze into small bowl and set aside. Measure 2 tablespoons glaze into small bowl and set aside. Whisk soy sauce and maple syrup in 13- by 9-inch baking dish until combined; carefully place fillets flesh-side down in single layer in marinade (do not coat salmon skin with marinade). Refrigerate while preparing grill.
Using chimney starter, ignite about 6 quarts
(1 large chimney, or 2 1/2 pounds) charcoal briquettes and burn until covered with layer of light gray ash, about 15 minutes. Empty coals into grill; build two-level fire by stacking two-thirds of coals in one half of grill and arranging remaining coals in single layer in other half. Position grill grate over coals, cover grill, and heat until grate is hot, about 5 minutes; scrape grill grate clean with grill brush.
Remove salmon from marinade and sprinkle flesh liberally with pepper. Using long-handled grill tongs, dip wad of paper towels in vegetable oil and wipe hot side of grill grate. Place fillets flesh-side down on hot side of grill and cook until grill-marked, about 1 minute. Using tongs, flip fillets skin-side down, still on hot side of grill; brush flesh with glaze and cook until salmon is opaque about halfway up thickness of fillets, 3 to 4 minutes.
Again using long-handled grill tongs, dip wad of paper towels in vegetable oil and wipe cooler side of grill grate. Brush flesh again with glaze, then turn fillets flesh-side down onto cooler side of grill; cook until deeply browned, crust has formed, and center of thickest part of fillet is still translucent when cut into with paring knife, about 1 1/2 minutes. Transfer fillets to platter, brush with reserved 2 tablespoons glaze, and serve immediately with lemon wedges.