I once tried that on a Raleigh. I eventually gave up trying to completely remove the paint. I used sand paper to break the sheen on the surface and just used the old paint as a "primer" coat. It worked well.

If you are determined to get it all off, perhaps wrapping with paper or foil will keep the solvents from evaporating before they soften the paint. Once softened, try scratching/scraping with a paint scraper.

Sand paper also works. If you want it to go faster, use a power sander. Be careful with a power sander.