the shop guy thought your bike has a mechanical
advance mechanism, with rotating weights and stuff,
but that isn't true, advance is done for each cylinder
individually, and in an electronically manner, done
by the kokusan ignition boxes.
i doubt that they both stuck at the same time,
not sure if they can stick at all, suppose you
should check either your carbs rubber connections
to their manifolds, or the carbs themselves.
I'm running pod filters and it does run lean at higher rpms.. I have a stage 2 jet kit coming so maybe a good cleaning and jetting will help..
I've checked the cables and the throttle returns fine.. wierd thing is that when i come to a stop, if i gear down into first gear and brake to lug the motor down below 3000 rpms sometimes makes the idle normal. Other times you can blip the throttle a few times and it will go ahead and idle down.