Hyosung GV650 Aquila / GT650 Comet FI Service Manual Supplement (2008)

Hyosung expanded beyond small-displacement motorcycles in the early 2000s with a family of liquid-cooled 647 cc V-twins. The GT650 Comet entered the market as a naked roadster in 2004 and helped establish the Korean manufacturer's presence in the middleweight class. Its steel-tube chassis, double-overhead-cam V-twin and six-speed gearbox offered a distinct alternative to the established Japanese middleweights. The family evolved to include the semi-faired GT650S and fully faired GT650R, giving riders a choice of everyday, sport-touring and sport-oriented bodywork around a shared engine platform.

The related GV650 Aquila arrived during 2005 with a different approach to the same 647 cc engine family. Unlike the GT's upright or sporting stance, the Aquila used a long, low cruiser chassis, forward-set controls and a larger 18-inch front wheel. Hyosung also selected a five-speed transmission and belt final drive for the GV650, whereas the Comet machines retained a six-speed gearbox and chain final drive. These differences meant that even motorcycles sharing the 81.5 mm bore and 62 mm stroke were not mechanically interchangeable across all chassis and drivetrain procedures.

Early production 650 models relied on carburetors, consistent with the service literature issued for the original GT650, the GT650S/GT650R and the GV650 in 2004–2005. In the late 2000s Hyosung developed fuel-injected versions, culminating in the June 2008 S&T Motors publication describing the Aquila 650 FI and three Comet 650 FI derivatives. This transition replaced carburetor metering with ECU-controlled injection, revised fuel delivery and sensor-based engine management. Fuel-injection diagnostics introduced electronic fault-code checks for such components as the throttle-position, intake-pressure, water-temperature, oxygen and tip-over sensors. A contemporary Hyosung 650 owners' technical history distinguishes the original carbureted motorcycles from the first EFI generation introduced around 2008.

Although the models remained recognizably related, the EFI update served different audiences. The Aquila kept its cruiser layout, five-speed transmission and belt drive, while the GT650 Comet continued as a six-speed naked motorcycle; the S and R models added increasing degrees of wind protection and sport-focused styling. The liquid-cooled DOHC 90-degree V-twin design and tubular-frame philosophy remained central to the fuel-injected 650 V-twin motorcycle family. During this era the manufacturer's publications carried the S&T Motors name, reflecting corporate developments alongside revisions to its motorcycles and their electrical and fuel-control systems.

The 2008 EFI generation sits between the earlier carbureted Comet/Aquila models and later revised EFI systems and bodywork. The change was significant for maintenance because ECU and sensor diagnostics, wiring and fuel-pump testing became different from the carbureted variants. For context, the Hyosung service manual catalog also contains earlier GT650, GT650S/GT650R and GV650 literature. Publication 99000-51310 is specifically a June 2008 factory supplement addressing EFI differences; it directs the technician to the previously issued carbureted-model service manuals for repair procedures it does not repeat. The 2008 date therefore identifies this manual's edition, not a guarantee that every later EFI motorcycle uses identical components.