You can use electrolysis to remove rust. For example you can use a 5 gallon electrolysis tank (plastic). Use Sodium Carbonate (Arm and Hammer Washing Soda), a 12 volt motorcycle battery charger, and a steel rod. Add 1/4 cup of A&H soda for every gallon of water. Electricity induces the chemical reaction so, you connect the negative lead on the rusty piece and the positive lead on the steel rod. The electricity induces the reaction to move the rust from the work/piece to the sacrificial steel rod. End result: Given enough time and electric current, the rust moves from the work to the rod. Electrolysis won't add metal back where it's been rusted away, but it will help stop the rust in it's tracks so you can paint and restore the metal. That tank looks like one from a 1996 CB750 I use to have.