| Spec | GX390 |
|---|---|
| Displacement | 389 cc |
| Bore × stroke | 88 × 64 mm |
| Net power | 11.7 hp (8.7 kW) @ 3,600 rpm |
| Net torque | 19.5 lb-ft (26.5 Nm) @ 2,500 rpm |
| Compression ratio | 8.2:1 |
| Oil capacity | 1.16 US qt (1.1 L) |
| Fuel tank | 6.4 US qt (6.1 L) |
| Dry weight | 69 lb (31.5 kg) |
| Ignition | Digital CDI, variable timing |
| Starting | Recoil / electric |
| Size (L × W × H, min) | 16.0 × 19.1 × 17.7 in (407 × 485 × 449 mm) |
Source: Honda Engines official specification pages (engines.honda.com/models/model-detail/x-large-gx), checked 2 Nov 2026. Power is SAE J1349 net output measured by Honda; engines installed in equipment may vary. This site is independent and not affiliated with Honda.
Oil: how much and how to check
The GX390 holds 1.16 US quarts (1.1 L). Honda engines are filled to the edge of the oil filler neck with the engine level – don’t screw the dipstick in to check, just rest it in the neck. Overfilling is as bad as running low: excess oil can foul the plug and push out through the breather.