With the spare carrier removed, a light surface rust can be seen in spots across the underside of my tank. This is an '81. The tank is galvanized.

So here's my question(s): Would it be a foolish waste of time to clean and paint these rusty spots with the tank in place? Is dropping the tank and doing a complete de-rust and re-paint the only reasonable approach? Is a little rust on the bottom always accompanied by the same (or more?) on top? And what about the inside? A check of the fuel filter has not revealed any significant debris, of the type that might indicate that the tank is rusting inside.

thanks for your time

 

The tank has a bladder inside, so there should not be any rust inside. As far as the outside, it wouldn't hurt to clean and re-paint it. Tanks are not trivial to remove, but not impossible either. Depends on how much work you want to put into it. If it isn't pitted, I would probably leave it alone.

 

But use something like "Por-15" or "Rust Bullet" to coat the outside of the tank.

 

I'm assuming you have the body off. If you do might as well de-rust and paint, if you don't, don't bother, it's not a big deal.