1978Xs400

Hello all, I am new here so lets see if you can help me. I have a 1978 xs400-2e, It was running rough and I rebuilt the carbs and cleaned averything good. It still ran rough. I took off the left plug and the bike stalled, I took off the right plug and it ran with very little difference. I took out the plug and started the bike and the spark is great,( I still see the blue dot in my eyes). The last thing I checked was the mixture screws. They had plastic caps to avoid anyone addjusting them, bot the strange thing is the the right carb screw had no tip on it. it was blunt. I looked in the carb and the tip broke off in the port. I can get it out, but I cant find a listing for the screw and all my books say the adjustment is pre-set. Most XS400's have 1 1/4 turns 132 main jet, but the XS400-2E has a 137.5 main jet and as I mensioned a preset mixture. I found a site that calls for the mixture screw to be yamaha p/n 20730-001. can anyone tell me where to get these or if there is a cross reference for the parts. the carbs are mikuni 34 with an ID mark of 2G5-60 Thanks for any help