Unfortunately, the odds are against you...but its not impossible.
Assuming that you have a tank from the early 70s, the original paint is likely an acrylic lacquer (thats what my 69, 70 and 71 CB750 tanks have). Although this paint has hardened over the past few decades, it is not anywhere as resilient as a modern poly urethane. Yet, it is likely that the dark metallic paint on top of the original paint is a more modern poly urethane. That means you might have a harder paint covering a softer paint. Thats problem number one.
Problem number two is that the original paint was likely sanded down a small bit to spray primer on it before applying the dark metallic paint (assuming the painter had a very basic understanding of paint). That means that your original paint might not be in great condition under there. Thats problem number two.
Problem number three is that in the early days, Honda often used very little or no clear coat on their paint. How do I know? Gently polishing original paint tanks from 1969 and 1970 will pull up some color. That tells me that it is either very thin clean paint or that the top candy coats were thinned and used as the top coat.
Ok, thats the bad news.
The good news is that you might have low quality dark metallic paint on the tank that did not adhere very well. That means that it might come up easily.
What would I do in this case? First, I would do everything I can to try to save the original paint. That means a few experiments on a hidden part of the tank to find your best plan. A few ideas for things to test:
- I would very very slowly try wet sanding down the tank on the bottom to figure out whats under there. Confirm that there is primer for example. Go slow so you don't burn through the original paint.
- Try some paint thinner. This is much more gentle than acetone and might soften the dark metallic paint. Again, do this in a hidden area.
- Drip a bit of fuel on the dark metallic paint. If you are very lucky, the dark metallic paint is not poly urethane and the paint will bubble. As long as you don't leave it there for very long, it shouldn't harm the original paint. Be careful with this as with the previous idea. Work in an area that if things go poorly, all hope isn't lost.
I do not suggest using paint stripper or acetone. They are too strong and will pull up your original paint very quickly.
I suspect that very careful wetsanding is your best bet.
