RE: Engine For Kwik FLi Mk. III
Ralph,
When I was into flying WWII airplanes we used to clean this old bomber we had in natural aluminum with an acid etch from the aviation parts house. I remember it was pretty hot so we mixed it about 1/4 acid to 3/4 water and applied it with washing brush. Rinsed it almost as soon as we got it on the surfaces.
I would think that if you continue to use what you have it'll clean that up. Trouble with going stronger is that you can go too far!
You might call the local airport and find a name of an aluminum acid etching compound for your purposes though.
Chris...