I just switched out the stock 37.5 idle jets for 40's on my '98 GS500, and if you haven't done so already, you need to *immediately*! 

My bike actually idles at 1100-1200 likes it's supposed to now, almost immediately after starting.  No more 20 mins of riding to let it warmup, stalling at lights, and constant idle screw adjustments.  Thank you forums for all the wisdom, and thank you Buddha for the jets!