Replacing the Nozzle & Venturi gasket kit will definitely help but is really only the first step to correcting the problem. You may also have to replace the main control valve seals. Easy enough to do but you will have to depressurize the softener. Also easy to do. There is a screen at the bottom of the Brine Valve assembly located in the Brine Well (4" diameter black tube in the salt tank) which has to be cleaned. Remove and dismantle the Brine Valve asm. to get to the screen.
Make sure there aren't any restrictions with the softener's drain (discharge) hose. No kinks, not crushed, no restrictions in the flow control in the drain elbow located on the right side of the main control valve.
Do the easy things first: drain hose, nozzle gasket kit and brine valve screen before servicing the main valve.
Remember, softeners generally work better with good water pressure. If you have a sediment filter installed in front of the softener, make sure it isn't plugged with dirt.
Hope this helps!