I searched the site - could not find much on the jet needle plate:

I love to wrench on my toys but have hesitated on my S40...being "new" and "under warranty" and all that.  I have surfed this board jealous of all the tips and tricks, wishing I had bought a used bike.  Then yesterday I decided screw it and pulled the seat, tank and began the famous white spacer mod - using 2 #4 washers (and replaced those crappy screws with SS allen heads).
2 questions: I didn't notice when I removed it...dimple up or dimple down on the jet needle plate?  I re-installed so the two holes at 5 o'clock and 7 o'clock are wide open...assuming this was right.  I think that meant the dimple was down.
Also, with a 10 mile test ride, I experienced MUCH more backfiring - although still not what I would call extreme.  I went from 2 or 3 backfires to 6 or 7. Although the power curve through mid-range seems brighter and more correct, I could lose the BF on decel and be happy.  Do you think once I turn out the (currently still plugged) low speed mixture screw it will improve?  (I like making only one change at a time - easier to trouble shoot)

California bike - 100% stock intake and exhaust.

Seea:  I can't help you with the carb problem but what is that bike in your profile?  The pic is too small to make out!

Good Luck!