sometimes it idles perfectly smooth at 750. sometimes it idles perfectly rough at 750. sometimes when i turn on the AC (i know it's no suppose to do this) it drops to 500, but stays smooth. stupid rotaries i'm unfamiliar with!

 

well droping with the A/c on would be a problems with the BAC.(I have one left for sale if you wish )

 

Yup, most likely but not necessarily the BAC. Before you replace do a "search" on BAC get cleaning directions and try first. Also use FSM to check its operation. Why spend bucks when 15 minutes might fix it.