Throttle kickdown is a transmission operation. The transmission senses a heavy throttle application and "kicks down" to a lower gear to improve acceleration. On the A-413, kickdown is actuated by a mechanism called the kickdown linkage or throttle pressure linkage. This mechanism likes to freeze up from disuse, so you don't have the kickdown function when you actually need it. I would recommend doing a cable adjustment and check to see if the linkage is frozen if you're doing transmission work. My linkage was frozen and the cable was out of adjustment, causing poor shift quality and erratic shifting. Any good manual should have info on how to do these procedures.