i think the choke may be a factor. it's likely not the only factor, but it is part of the whole picture.
everybody i know here in LA that daily's anything runs a choke. it's only the fun summer time burger cruiser guys that generally don't, but for all my clients i tell 'em to run a choke.
there's also the fact that two weeks ago it was 100+ and dry and now it's much cooler and damp. so again, not the only issue, but a consideration.
i think you're headed in the right direction. see if you can dial in your advance/curve better. how do the plugs look?