Can too Much Sugar affect a Hummingbird?

I love our hummingbirds that come to our house! We make them homemade nectar and because we have so many hummingbirds coming to our house, we have 3 feeders and use a Milk carton for the juice (which OF COURSE is sterlized). We use about 4 cups of sugar. But if we use MORE sugar, can it affect or possible kill the pretty hummingbird(s)?