Analog film photography and cameras

you won't get sharp with a pinhole. I can't remember the formula but the optimum sharpness is a balance between small (smaller=sharper in general, since light travels in straight lines) and not too small (you start to get diffraction since light is a wave). it's probably online somewhere, it's not too difficult to work out using a typical wavelength of visible light and the distance between pinhole and film.
what helps is having the pinhole as thin as possible, but you probably know that. are you using thin brass sheet? sand it down thinner where the pinhole is (so long as it doesn't become translucent) and take off any burrs from making the hole.
beyond that, the non-sharpness is one of the joys of pinholes - nothing is in 'focus' but everything is just as sharp, from foreground to distant.

These are not very sharp, any ideas how to improve the results with a pinhole?

I have made rather big pinhole cameras out of shoe-boxes (exposing paper) as well as tiny ones out of matchboxes (exposing film).
Of course the "negatives" from the shoe boxes were huge but I've always found I get sharper results with bigger boxes.
I also tried, like you, making a lenscap-pinhole (but with DSLRs) - never turned out well.

The only tip I can give you regarding the pinhole itself is that I had best results with pieces of red bull type cans, making a bump (not a hole) in it with a needle, then sanding the bump with fine sandpaper in circles until you "open" the bump. Check for burrs with a loupe.

Good luck!

Ps: If you haven't yet go build a shoebox-one! It's big fun!