Actually I finally figured out that the motor housing has to be removed to get to a tension screw (visible when the bowl rack is lowered fully) and screw it in from the inside (housing cap screws hidden under a metal strap that is loosened from the back; remove the top; three screws hold the motor housing to the neck/base). It's virtually impossible to get to from the bottom. The three screws holding the motor housing are not easy to get to but mercifully easy to loosen at a slight angle. Once that's off, the adjustment screw can be inserted more easily. Thanks to those who responded!