Fuel Injector

This aftermarket fuel injector is engineered for the SYM Symphony 125I ST 125cc fuel injection system, covering 2017-2020 model years with OEM cross-reference 06414-HKK-000. As the final control element in the engine management system, the fuel injector’s performance directly impacts starting behavior, idle quality, fuel economy, and exhaust emissions.

The injector mounts on the intake manifold with its nozzle tip positioned to spray fuel directly onto the back of the intake valve head. When the ECU energizes the solenoid coil, the magnetic field lifts a precision-machined needle valve from its seat in 1-2 milliseconds, allowing pressurized fuel to flow through a multi-hole disc nozzle. The resulting spray consists of droplets sized 50-80 microns, small enough to vaporize completely in the hot intake air before the valve opens. At 3.5 bar operating pressure, the injector delivers 180-220 cc of fuel per minute at full duty cycle, with pulse widths ranging from 2ms at idle to 12ms at wide-open throttle.

The solenoid coil is wound with 0.5mm copper magnet wire to achieve a resistance of 12-14 ohms, compatible with the ECU’s 12V drive circuit. The needle valve and seat are manufactured from 440C stainless steel, hardened to 58 HRC and lapped to a sealing surface finish below 0.1μm. This precision ensures complete shutoff when de-energized, preventing the fuel drip that causes rough idle and hydrocarbon emissions. The O-ring seals are manufactured from Viton fluorocarbon elastomer, resistant to modern oxygenated fuels and temperature excursions to 150°C.

Technical specifications: flow rate 180-220 cc/min at 3.5 bar; spray pattern: 4-hole cone 15° included angle; coil resistance 12-14 ohms; operating pressure 3.0-3.5 bar; seal material Viton FKM; connector: 2-pin sealed automotive type.

Common symptoms of injector failure include: hard starting when cold (due to poor atomization at low battery voltage), erratic idle speed fluctuating more than ±200 RPM, decreased fuel economy exceeding 15% from uneven cylinder filling, and diagnostic trouble codes P0171 (system too lean) or P0172 (system too rich). Before replacement, verify fuel pressure with a gauge and inspect the electrical connector for corrosion. Always replace the injector O-rings and manifold gasket during installation, and run the fuel pump to check for leaks before starting the engine.