As herbfargus said, the ‘insert coin’ button doesn’t work as the ‘hotkey’ function is bound to the same button. Since you can’t change the ‘insert coin’ button, you’ll need to change the ‘hotkey’ button – I use a 360 controller for most arcade titles, and I find the XBox button on that works well (it doesn’t bind it to anything by itself, but if you’re editing the retroarch controller config it’s button 10). The problem only occurs on some games and not others, but it’s always the same games so I guess it’s something to do with what arcade hardware they ran on or something.
As far as the other games not running, there are two main possibilities:
– You need the right romset for the version of MAME you’re using (or in this case, FBA). There’s some good help on this wiki page: https://github.com/RetroPie/RetroPie-Setup/wiki/Managing-ROMs
Using clrmamepro to make sure the right roms are in the right places can be a bit tricky for the beginner, but there’s some good guides around.
– The other possibility is that some games need another file in the rom folder with them – a BIOS for the arcade hardware it ran on. The most common one is for games that run on the Neo Geo – you need neogeo.zip in the same folder as the ROM or they won’t work. On your list, the Metal Slug games definitely need neogeo.zip.
While there’s nothing like the MAME onscreen menu in fba-libretro, you can get into the game’s settings. If you go into the Retroarch menu and go to Core Options, you’ll see two options called “Diagnostics” and “Neo Geo Unibios”. Try toggling them on and off in different combinations, exiting the menu back to the game in between each try – I’ve not figured out exactly what combination is the right one.
When you get it right, the game’s settings menu will pop up as soon as you exit the Retroarch menu. You can then change setting such as difficulty, how many coins per play, how many points for an extra life and so on. Sometimes it’ll save the settings for the next time you start the emulator, sometimes it won’t – it depends on what arcade hardware the original game was on (which is annoying, as I really want to turn the red blood on in the Metal Slug games and it won’t save the settings for Neo Geo games!)
Hope that’s helpful,
(EDIT: I just remembered, if you want to look up specific games and see whether they’re parents or clones, progettoemma.net is a really useful site with plenty of information about every game.)