VN750Rider/Jerry· Premium Member
Muriatic (hydrochloric) acid is stronger than phosphoric acid (usually found in toiler bowl cleaners) and does a much better job removing rust especially if it is really bad. I have done about 5 tanks with muriatic acid. I removed the petcock and plugged the opening (muriatic acid will eat aluminum in minutes). I washed out all the old oily residue and gas deposits with a product called Castrol Superclean, rinsed it good, left the cap off and let it dry, then completely filled the tanks with muriatic acid, let soak 24 hours, and dumped it out. ALL the rust was gone. No putting nuts or rocks inside or shaking or anything like that, just a 24 hour soak in full strength muriatic acid. One tank did develop a couple of pinhole leaks, as it was already rusted through and the rust was plugging up the holes. I coated the inside of that one with POR-15, and used it for a couple of years. IMO, if the tank doesn't leak, DON'T coat it with anything. And don't use Kreem even if it does leak. On the Vulcan 750, the fuel gauge sending unit would also have to be removed, and the hole in the bottom sealed somehow. Muriatic acid only reacts with metal, it will not harm plastic or glass. Wear latex gloves, eye protection, and avoid breathing it the best you can. It must be used with care, but it WILL remove all the rust. It will not remove tank sealer, as it is not metal. Adhesive remover will get some of it out, as will acetone, MEK, and a few other chemicals, but I know of no way to get it all out. Motorcycle restorers hate the stuff. They usually cut the bottom out of the tank, remove it manually, then weld the tank back together, a VERY expensive job. To me a lined tank is a ruined tank.