In a large bowl, combine cake mix, pudding mix, 1/2 cup Irish whiskey, and oil. Add eggs and beat at medium speed with an electric mixer for 4 minutes, scraping down sides of bowl as necessary. Spoon into greased and floured 10-inch Bundt or tube pan.
Bake in a preheated 350-degree oven for about 45 minutes, or until a cake tester comes out clean. When cake is almost done, prepare syrup. Combine sugar, butter, water, and lemon juice in a small heavy saucepan. Bring to a boil slowly, stirring until sugar is dissolved. Remove from heat and stir in remaining 1/4 cup Irish whiskey.
Turn cake out onto two large sheets of aluminum foil placed together to form the shape of a cross. Let cake cool for 10 minutes, top side up for tube cake and upside down for Bundt cake. Using a skewer, make holes all over top and sides of hot cake. Drizzle syrup very slowly over cake, being careful that too much does not run into any cracks on top of cake. Bring foil up around cake and wrap securely.
Cake may be served when completely cool, or store in an airtight container overnight. Cake may be wrapped securely in foil and stored in the refrigerator for several weeks or in a freezer for up to six months. Serve with whipped cream.