Clean any dirt or debris from the throttle on the engine. Locate the throttle by following the throttle cable from the handle of the mower to the throttle itself.
Spray the throttle with a spray lubricant. Wipe any excess lubricant away from the throttle.
Push on the throttle with a screwdriver to move it back and forth and get the lubricant working.
Locate the throttle adjustment on the underside of the throttle handle, where the cable meets the handle. Turn it to adjust the cable so it is taut. A loose cable will not move the throttle.