This invention relates to a lawn mower. In certain example embodiments, the lawn mower may be of the walk-behind type. In certain example embodiments of this invention, the lawn mower may have one or more of: (a) an improved handlebar weldment assembly, (b) an improved operator presence control (OPC) system and structure, (c) an improved speed control system structure, (d) an improve cam bar system for hydraulic pump control, (e) a return-to-neutral biasing system that biases hand lever(s) toward a neutral position but only from a reverse position (not from a forward position), and/or (f) an improved tracking adjustment system.