A pump apparatus for an adjustable metering and dispensing pump apparatus for food products including a product piston moving in a product cylinder, the product cylinder being connected to a food hopper and a dispensing nozzle. The pump apparatus also includes a cylindrical valve moving within a central aperture in the product piston to selectively open and close passageways also in the product piston which communicate with intake and outlet ports connected to the product cylinder. The valve is attached to a valve piston moving within a valve piston cylinder and the valve piston cylinder is attached to a source of compressed air, to a sensor and to a control assembly. The control in turn is connected to a foot switch to allow an operator to initiate a cycle of the pump apparatus. The valve piston reciprocates both the valve piston and the product piston, however, while the valve moves directly with the valve piston, the product piston is connected with a lateral pin mounted in an elongated lateral slot formed in the product piston resulting in a delayed movement of the product piston. A screw is mounted to the valve piston cylinder to abut the valve piston in an adjustable manner so that the valve piston stroke is changeable resulting in a corresponding change in the volume of a food product in a product chamber in the product cylinder.