It's possible they are both just out of tune as well. If your rich on the LSN your idle gap is most likely open too far which can cause the high rev followed by dropping down. I would suggest on the RB that you open the throttle ALL the way and hold it open, close the LSN and then back it out 5 turns. Close the HSN and back it out 3.5 turns. Now pull off the air filter and remove the venturi from the carb and set your idle gap so that it's open about the thickness of a credit card (between .6 - .9 mm) This will probably be rich and will want to load up and die so lean the LSN till it will idle good. Now tune the HSN till it runs well up top. You may need to make some more small adjustments to the LSN and possibly the idle but they should be small adjustments.