Remove and empty the bag on the Simplicity mower as needed while mowing. The frequency depends on the size of your lawn. Emptying the bag often prevents the bag from getting clogged with too many clippings. If that occurs, the suction does not work correctly to collect the grass and other debris from the lawn.
Clean out the chute of the Simplicity mower as well when you empty the bag. Wear sturdy work gloves when doing it. The chute is near the area where you attach the lawn mower bag to the machine. Even with an empty bag, if the chute is clogged, the bag will not fill properly. This causes unnecessary stress on the motor.
Adjust the throttle setting on your Simplicity mower to the highest speed. If the engine settings are incorrect, you bag might not fill properly.
Inspect the Simplicity mower blades. If they are coated with debris, bent, loose or dull, the bag won't fill properly.