I went looking for the infamous 'EPA plug', and found that it had already been removed.  It may be hard to see in this photo, but the idle mixture screw actually stands slightly proud of the hole, such that it looks like no plug could ever have been there.  I wondered if this meant that my bike was running scandalously rich, so I counted the turns it took to fully seat the screw.  I expected 4-5 turns, but it was only 1 3/4 turns!  I then backed the screw back out to the original position and went further to 2 full turns out.  This seems to have cleared up the tendency of the bike to die when I close the throttle abruptly.  So, was she actually running a bit lean?  Has anyone seen an idle mixture screw like this before?