[speedshopmike]

1st, at this point please start with a new plug so you can see it well.
to answer, because the motor's always running on the pilot (where it won't clean out well) but isnt up on the main until higher speed/throttle opening.
(and/or could have weak spark)
if you have a good camera and light, post some pics of the plug if you like, but i'd start fresh first.
even the 100 could be too fat, btw; i'm not saying it isnt, or could be lean.
only discussing that dying off idle usually indicates it's lean there.
you could experiment by fattening the heck outta the idle mix with the small pilot in and see if it helps before you drill it.
the extra fuel from the idle circuit will *partially cover up the lean sag.
you can also raise the needle up a position at a time; that''ll bring in the enrichment sooner.
also, needles with different tapers are available.