| MODEL | YAMAHA GX 400SP 1978 - 1979 |
| Year | 1978 - 1979 |
| Engine Type | Four stroke, parallel twin |
| Displacement / Capacity | 391 cc |
| Bore X Stroke | 69 x 52.4 mm |
| Compression Ratio | 9.2:1 |
| Cooling System | Air cooled |
| Max Power | 37 hp @ 8800 rpm |
| Max Torque | 3.2 kgf-m @ 8000 rpm |
| Ignition | — |
| Induction | Carburetor |
| Start System | Kick |
| TRANSMISSION SPECS | |
| Lubrication | — |
| Gear Box | 6 Speed |
| Clutch | — |
| Final Drive | Chain |
| CHASSIS SPECS | |
| Frame | — |
| Front Suspension | Telescopic forks |
| Rear Suspension | Dual shocks |
| Front Brakes | Single disc |
| Rear Brakes | Single disc |
| DIMENSION SPECS | |
| Overall Length | — |
| Overall Width | — |
| Overall Height | — |
| Seat Height | — |
| Wheelbase | — |
| Ground Clearance | — |
| Dry Weight | 168 kg |
| Wet Weight | — |
| WHEEL SPECS | |
| Front Tyre | 3.00-18 |
| Rear Tyre | 3.50-18 |
| FUEL SYSTEM | |
| Fuel Capacity | — |
| Fuel Consumption | — |
| Top Speed | — |
The GX 400SP continued the 400 twin for 1978 and 1979 with the same engine and cycle parts as the 1977 bike. It served as a lightweight sporting road machine in Yamaha's late-1970s range.
