Crush completely the strawberries, mash bananas and combine fruit. Measure 4 cups of fruit mixture into a saucepan; add lemon juice.
Mix fruit pectin into saucepan; place over high heat. Stir until mixture comes to a hard boil. Immediately add all sugar and stir.
Bring to a full rolling boil. Boil hard for 1 minute, stirring constantly. Remove from heat. Skim off foam; stir and skim for 5 minutes. Ladle into jars at once; cover with 1/8-inch paraffin wax or process in a boiling water bath for 10 minutes.