Actually lean out. Play around with leaner air screw, needle position, pilot, one or a combination should raise your idle so you can lower the slide/idle screw.
I've found with mine that the decel noise was associated too much slide height at idle. (Idle screw turned too far in). You might need to tweak needle? Pilot? air screw? to get the proper idle with less slide height/idle screw.
Still riding the EC250
I'm still running my updated 2000 EC250. It's been a great bike and super reliable. The suspension has gone thru a couple different tuners. New bikes always look so tempting but this still gets it done.