Had space(more than 1px) between letters with custom font

I guess the font tool adds just 1px of padding, and it isn't configurable. Unfortunately it looks like it's server-side so you can't easily fix that. You could use the command-line tool that i originally made, and could modify the place where that adds an extra column? https://github.com/espruino/Espruino/blob/master/scripts/create_custom_font.js#L58

I guess what you could do is use Espruino to re-encode the fonts yourself. I'll see if I can come up with an example.

Your use of g.stringWidth looks like it should work fine - could you maybe print the values you're getting from it and see if they are changing?