I've got an 80 model 250 that I am restoring, and my stock carb was like yours, no idle screw. Just the way they made them back then.....My stock carb was rich also, but the bike had been sitting up for about 9 years before I got it. Parts inside the carb had corroded and a section of the float bowl baffle plate had totally rusted away! I found a new carb for it on ebay, and that things run like a top now, and has an idle screw as well! As for the reeds, my engine has them. I wonder if someone took yours out, before you got the bike?