The gasket on the carburetor seat is as good as bonded. (The air horn gasket came off whole, looks good enough to re-use, which I didn’t). I’ve scraped for an hour, dissolved what I could with carburetor cleaner, tried every other nasty solvent I have on hand. All the fiber is gone; I’m down to a shiny brown layer - it looks like varnish.
A few places on-line mention ‘gasket removal solvent’; one mentions Loctite brand, of which I can find no mention on loctite.com. I can’t find any at the auto stores.