I figured I'd see if plugging the hose to stepper motor could eliminate the popping on overun and it did. However, the bike runs completely different and that is all I changed. There seems to be some constant vibration coming from the engine, like that from a four stroke dirt bike, but not as severe.
Recently I did the valves, sync throttle bodies new fluids and plugs, fuel filter and air filter.
I am running 2230bd00 1200 2v non ABS map with lambda AKA O2 sensor on. Perhaps I should try 2230bd01 because if I recall the ignition was advanced and see how that does. Before that I'll double check the throttle bodies and see if they are still synced.
I do not find the vibration uncomfortable, but I am concerned it is detonating the fuel at the wrong time and could cause harm to the engine.
Throttle response had improved and is excellent at low to mid range with a noticeable increase in torque simply by plugging the stepper hose going to the air filter. It does not like to rev as much as before above 7k rpm, but I'm rarely in that range.
Overall, I guess I have to decide if some burble on decel and a little less torque is better than more torque and some possible damaging vibrations.
Also, I lost a nut on my shifter linkage during that test ride.