The first photo with the two arrows pointing at screws are the correct location, one on each carb.
You adjust these in and out whilst listening with a peice of garden hose, or something of similiar bore. One end at your ear, the other close (but not actually in) to the bellmouth. Keep doing this till you get an even sound across all four throats.
If your idle was previously OK, it would suggest something has fallen off, or moved. Check your linkage thoroughly plus other things like your distributor timing. Perhaps the timing has shifted? The idle screws won't move on their own so probably something esle like a return spring falling off etc.
