A, STD, and B modes only affect the throttle response on the RN22/23. A reaches wide open throttle at a more aggressive rate than STD, B is limited to 77.4% throttle and has a slower rate than STD. Ignition maps and fuel maps are the same for all three modes.

On the RN23 throttle is cut back at 12.000 RPMs to 83.6%

Hope this helps.