I bought this bike and have had trouble with the carbs. They have recently been rebuilt and when i got it i know they were never sync'ed. I was bogging real bad about 4500-5000rpm, i failed emissions for too rich a mixture. I have tried to use the clymer manual but the setting they say is a good starting point gives worse result than when i got it. no mods on the bike and have tuned it by ear riding along with screwdriver in pocket to stop and adjust here and there, but still lacks in the top end. Have ordered carb sync tool. waiting on its arrival, but wondered if anyone has any secret tip or trick fot this. gonna also run individual cone filters instead if the large airbox. Any help is much appreciated!

 

I have an 82 GS 650e and I have the same problem...and have rebuilt the carbs 6 times.....now I think it may be the sync problem you are having....
I have replaced the diaphrams as well and it hasn't helped