I've done several with Kreem cause that's what PU sells. One with POR that the customer brought in. Biggest thing is do it right or don't bother, follow the directions, prep is key.
How rusty? If it is just a little, leave it and use an in-line filter. I would only prepare and coat the tank if the rust is excessive. Folks have more issues with coatings than they would had they left the tank alone and dealt with the small amount of rust that might eventually leave the tank and seek to enter the fuel system. If possible, put a low spot (loop) in the fuel line between the tank and the filter. Whatever rust comes out will settle in the low spot, and you can occasionally disconnect the line and drain that bit of sediment. Cheers, Dave
It's not my bike. It belongs to the local bicycle shop owner. It's just a "get it running so I can sell it" kind of project: carbs, tank, battery, fluids, etc.
Acids strip all coatings and leaves a bare surface that WILL rust. If you use Evaporust, it’ll safely remove the rust and leave any anti-corrosion properties intact. Also, it’s environmentally safe and won’t harm paint. I use coated deck screws as an agitator. Reposition and shake the tank every morning and you’ll eventually get the whole interior cleaned.
Or, just get a big tote, fill with diluted Evaporust (50% or so) and just submerge the tank completely. Rotate periodically to avoid air pockets not getting treated and just let it eat for a week or two. Pull off any aluminum bits like petcocks/etc before doing this.