Yamaha 25B / 30H two-stroke service guide
Oil, gear oil, spark plugs and the service schedule for the Yamaha 25B / 30H two-stroke (25 to 30 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.
Models covered: 25BMH and 30HMH two-stroke twins, worldwide names only (no USA or Canada names are listed): 2 cylinders, 496 cm³ (30.3 cu in), 72.0 x 61.0 mm, one carburetor, manual start, premixed gasoline and oil. 25BMH approval model code 61R, starting serial S: 020101, L: 350101; 30HMH approval model code 61T, starting serial S: 050101.
Quick answers
- What two-stroke oil does a Yamaha 25B / 30H two-stroke use?
- 2 stroke outboard engine oil, grade TC-W3.
- What is the fuel to oil ratio for a Yamaha 25B / 30H two-stroke?
- Mixing ratio 100:1, unleaded regular gasoline.
- What gear oil does a Yamaha 25B / 30H two-stroke use, and how much?
- Hypoid gear oil, SAE #90 (API GL-4). Quantity: 320 cm³ (10.8 US oz, 11.3 Imp oz); fill through the drain hole until oil flows out of the check hole with no air bubbles.
- What spark plug does a Yamaha 25B / 30H two-stroke use?
- 25B: NGK BR7HS-10; 30H: NGK BR8HS-10; qty 2. Gap: 0.9 to 1.0 mm (0.035 to 0.039 in).
- How often should a Yamaha 25B / 30H two-stroke be serviced?
- The factory schedule lists: Initial 10 hours; Initial 50 hours (3 months); Every 100 hours (6 months); Every 200 hours (1 year). In Hawaiʻi's salt water we do a full yearly service every 200 hours or 1 year, whichever comes first, and a new engine needs its first (break-in) service.
- When should the water pump impeller be replaced on a Yamaha 25B / 30H two-stroke?
- The factory schedule gives no replacement interval. In Hawaiʻi's warm salt water we replace it every 200 hours or 1 year, whichever comes first, because a worn impeller is the most common cause of overheating.
- What is the idle speed of a Yamaha 25B / 30H two-stroke?
- 1,100 ± 50 r/min; pilot screw 1-1/4 ± 3/4 turns out.
- What is the propeller nut torque on a Yamaha 25B / 30H two-stroke?
- 35 N·m (3.5 kgf·m, 26 ft·lb).
Maintenance specs
| Two-stroke engine oil | 2 stroke outboard engine oil, grade TC-W3 |
|---|---|
| Fuel to oil ratio | Mixing ratio 100:1, unleaded regular gasoline. |
| Gear oil | Hypoid gear oil, SAE #90 (API GL-4) |
| Gear oil quantity | 320 cm³ (10.8 US oz, 11.3 Imp oz); fill through the drain hole until oil flows out of the check hole with no air bubbles |
| Gear oil drain and check screws | Install the level check screw first, then quickly install the drain screw |
| Lower unit holding pressure | 100 kPa (1.0 kg/cm², 14.5 psi) for 10 seconds at the check hole; do not overpressurize. Leakage tester 90890-06762 |
| Spark plug | 25B: NGK BR7HS-10; 30H: NGK BR8HS-10; qty 2 |
| Spark plug gap | 0.9 to 1.0 mm (0.035 to 0.039 in) |
| Spark plug torque (M14) | 25 N·m (2.5 kgf·m, 18 ft·lb); without a torque wrench, 1/4 to 1/2 turn past finger tight |
| Idle speed | 1,100 ± 50 r/min; pilot screw 1-1/4 ± 3/4 turns out |
| Thermostat | Opens at 48 to 52 °C (118 to 126 °F); fully open at 60 °C (140 °F); minimum valve lift 3 mm (0.12 in); thermostat cover bolts 8 N·m (0.8 kgf·m, 5.9 ft·lb), always a new gasket |
| Propeller nut | 35 N·m (3.5 kgf·m, 26 ft·lb) |
| Power trim and tilt | None: manual tilt, tilt angles 4, 8, 12, 16, 20 degrees |
Service schedule
The factory maintenance intervals, with what is replaced and what is checked at each. Rows marked Hawaiʻi are our shop's yearly service for salt water use.
Initial 10 hours
Replace: gear case oil, gear case plug gaskets
Check: spark plugs, fuel filter, anodes
Initial 50 hours (3 months)
Replace: gear case plug gaskets, propeller cotter pin
Check: spark plugs, fuel filter, anodes
Every 100 hours (6 months)
Replace: gear case oil, gear case plug gaskets, propeller cotter pin
Check: spark plugs, fuel filter, anodes
Every 200 hours (1 year)
Replace: gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller
Check: spark plugs, fuel filter, anodes
We replace the water pump impeller at every service from 200 hours up, which can be sooner than the factory schedule, because of Hawaiʻi’s warm salt water.
Source: Yamaha 25BMH, 30HMH service manual, 69R-28197-ZA-C1. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.