A variable stroke mechanism was developed to optimize the efficiency of wind powered water pumping systems, by widening the range of efficient operation. The mechanism maintains the system near optimum operating efficiency by varying the stroke of a reciprocating pump to regulate the load on the turbine as the wind speed changes. Computer program was developed to optimize the design, and a prototype of the optimized device was constructed and tested. There were small differences between experimental and theoretical results obtained from the computer optimization program. Variation of the stroke length was observed over typical rotational speed ranges, generally from 150 to 275 RPM. Small differences between theoretical and experimental results can be related to friction forces as well as to the mass distribution of certain members, which were not taken into account in the computer program. Further laboratory testing of a modified version of the mechanism, as well as full scale field experimentation, should be performed to provide a more thorough evaluation of the complete wind powered water pumping system.