Preheat oven to 400°F. Butter 13 x 9 x 2-inch glass baking dish. Bring large pot of salted water to boil. Add yams. Cook until water returns to simmer, about 4 minutes. Drain. Rinse under cold water.
Arrange yams in prepared dish, overlapping slightly. Season with salt. Pour syrup over yams. Dot with 3 tablespoons butter. Cover and bake until yams are almost tender, about 25 minutes.
Mix flour and brown sugar in medium bowl. Add remaining 5 tablespoons butter. Rub in with fingers until mixture resembles coarse meal. Mix in pecans.
Sprinkle pecan mixture atop yams. Bake yams until tender, about 20 minutes. (Can be made 2 hours ahead. Cool. Cover and let stand at room temperature. Rewarm, uncovered, in 375°F oven 20 minutes.)