Before trying this, I was extremely skeptical about using 7-Up in a cake. But it works (and yes, you can use any lemon-lime soda).  The amount of lemon extract also looks alarming, but 2 tablespoons is the correct amount.

1 1/2 cups (3 sticks) butter
3 cups sugar
3 cups flour
5 eggs
2 tablespoons lemon extract
3/4 cup 7-Up

Cream together butter and sugar until light and fluffy. Add eggs 1 at a time. Blend in flour and lemon extract. Fold in 7-Up. Pour into a well-buttered 12 cup bundt pan. Bake for 1 1/4 hours at 325 degrees. Serves 8.