Fuel Injector Cap Assy.

This aftermarket fuel injector cap assembly is manufactured for the SYM Symphony 125I ST 125cc fuel injection system, compatible with 2017-2020 model years and cross-referenced to OEM number 17120-XJA-000. While often overlooked during service, the injector cap provides essential protection for the fuel injector’s electrical connector and spray tip, shielding these sensitive components from road debris, water ingress, and thermal damage.

The cap assembly mounts over the fuel injector body, creating a protective shroud that prevents direct exposure to pressure washer spray, road salt, and gravel impact. The upper portion covers the electrical connector, maintaining the seal integrity of the 2-pin automotive connector by preventing water wicking along the wire insulation. The lower portion surrounds the injector nozzle and O-ring seals, reducing thermal cycling stress by shielding the injector body from radiant heat emitted by the cylinder head during sustained high-load operation.

Manufactured from heat-stabilized polyamide 6 (PA6-HS) with a continuous service temperature of 150°C, the cap resists the thermal aging that causes embrittlement in standard plastics. The material formulation includes 15% glass fiber reinforcement for structural rigidity and UV stabilizers to prevent chalking and cracking from sun exposure. The retaining clip is molded from 30% glass-filled PBT with a stainless steel spring insert that maintains 15N minimum retention force after 100,000 vibration cycles.

Technical specifications: body material PA6-HS, heat-stabilized; clip material PBT-GF30 with 304 stainless steel spring; temperature range -40°C to 150°C; retention force >15N; color: black (UV-stabilized); weight 25g.

The cap assembly is designed for tool-free installation and removal, allowing quick injector service access. The clip mechanism engages with a molded boss on the intake manifold, providing positive retention that prevents cap loss under the severe vibration environment of a single-cylinder engine. The design includes a drain channel that directs any accumulated condensation away from the electrical connector.

Replace the cap assembly when: the retaining clip shows fatigue or loss of spring tension, the body is cracked from impact or thermal cycling, the mounting tabs are broken from improper removal, or during any injector replacement to ensure proper protection for the new component. Always verify that the cap seats fully and the clip engages with an audible click. A loose cap can fall into the road and expose the injector to damage, while an improperly seated cap may trap heat and accelerate injector O-ring degradation.