A pump-end control technology for pump-nozzle fuel supply unit, in which the pump is driven and controlled electrically for pressurizing and metering the fuel fed into an engine, is studied. The unit is composed of a solenoid driven plunger pump, a high-pressure fuel tube, and an auto-open nozzle, and only the pump is propelled by PWM power from an ECU. To achieve a higher metering accuracy, a metering theory deciding the fuel discharging rate was developed by studying the system using a physical-mathematical model. The developed so called T3 theory makes the fuel supply unit with excellent metering consistency under various conditions, which can meet the requirement of fuel supply unit application to small engine management system. The study reveals that an electrically characterized variable, T3, which is associated with the net output energy, can directly results in a mass discharge. Study of dimensionless variable T3 laid a foundation of a whole-state liquid measurement model, which is free from state variation. Experiments on a scooter with the system showed that the fuel supply unit along with the T3 metering theory was able to control the fuel-air ratio precisely to achieve good performances and low exhaust emissions, which indicates that the system has more advantages over fuel rail injection system in its systematic simplicity and integrity, low electrical consumption, and feasibility for layout on a developed scooter model.