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Tohatsu M25C2 / M30A3 two-stroke (429 cc twin) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu M25C2 / M30A3 two-stroke (429 cc twin) (25 to 30 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Tohatsu M25C2 and M30A3. 2 cylinders, 429 cc (26.18 cu in), bore 68 x stroke 59 mm. M25C2 25 PS (24.6 HP), M30A3 30 PS (29.6 HP), maximum speed running range 4,800 to 5,500 rpm. Gasoline oil mixture 50:1, water cooled (rotary rubber impeller) with a thermostat and relief valve, self recoil hand starter (electric starters optional), Keihin carburetor, dog clutch forward, neutral, reverse, gear reduction 12:23, through hub exhaust, 24 L separate tank. Premix, no oil injection.

Quick answers

What two-stroke oil does a Tohatsu M25C2 / M30A3 two-stroke use?
TOHATSU outboard motor oil or oil recommended by TOHATSU.
What is the fuel to oil ratio for a Tohatsu M25C2 / M30A3 two-stroke?
Gasoline oil mixture 50:1. Breaking-in after engine parts are replaced: 20:1 for 10 hours.
What gear oil does a Tohatsu M25C2 / M30A3 two-stroke use, and how much?
Recommended gear oil GL5 #80. Quantity: Approx. 250 cc (1/2 US pt, 1/2 imp pt). Pour oil in the lower hole until it appears at the upper plug hole.
What spark plug does a Tohatsu M25C2 / M30A3 two-stroke use?
NGK B7HS-10 or Champion L-82C10, qty 2. Gap: 0.9 to 1.0 mm (0.035 to 0.039 in); limit over 1.25 mm (0.049 in).
How often should a Tohatsu M25C2 / M30A3 two-stroke be serviced?
The factory schedule lists: Initial 10 hours; Every 50 hours; Every 100 hours; Every 200 hours or 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 Tohatsu M25C2 / M30A3 two-stroke?
The factory schedule says to replace it at 200 hours, and we follow that. In any case we never let it go longer than a year in Hawaiʻi's salt water.
What is the idle speed of a Tohatsu M25C2 / M30A3 two-stroke?
900 to 950 rpm with the clutch in.
What is the propeller nut torque on a Tohatsu M25C2 / M30A3 two-stroke?
29.4 to 39.2 N·m (3.0 to 4.0 kg-m, 21.7 to 28.9 ft-lb). Held with a split pin. Recommended rpm range 4800 to 5500.

Maintenance specs

Two-stroke oilTOHATSU outboard motor oil or oil recommended by TOHATSU
Fuel to oil mixGasoline oil mixture 50:1. Breaking-in after engine parts are replaced: 20:1 for 10 hours
Gear oilRecommended gear oil GL5 #80
Gear oil quantityApprox. 250 cc (1/2 US pt, 1/2 imp pt). Pour oil in the lower hole until it appears at the upper plug hole
Gear oil upper and lower oil plugs2 oil plugs, above and below the gear case.
Spark plugNGK B7HS-10 or Champion L-82C10, qty 2
Spark plug gap0.9 to 1.0 mm (0.035 to 0.039 in); limit over 1.25 mm (0.049 in)
Spark plug torque25 to 29 N·m (2.5 to 3.0 kg-m, 18 to 22 ft-lb), 14 mm
Idle speed900 to 950 rpm with the clutch in.
ThermostatWax type with pressure relief valve; opens at 50.5 to 53.5 °C, fully open at 65 °C (149 °F), lift 3.0 mm (0.118 in) when fully opened
AnodesTwo sacrificial anodes, one of them on the engine block. Check for corrosion and abrasion in every use; replace if required
Propeller nut29.4 to 39.2 N·m (3.0 to 4.0 kg-m, 21.7 to 28.9 ft-lb). Held with a split pin. Recommended rpm range 4800 to 5500

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.

  1. Initial 10 hours

    Replace: gear case oil, gear case plug gaskets, propeller cotter pin

  2. Every 50 hours

    Replace: gear case plug gaskets, propeller cotter pin

    Check: spark plugs, fuel filter, gear case oil

  3. Every 100 hours

    Replace: gear case plug gaskets, propeller cotter pin

    Check: spark plugs, fuel filter, gear case oil

  4. Every 200 hours or 1 year

    Replace: gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller

    Check: spark plugs, fuel filter

Source: Tohatsu M25C2/M30A3 service manual, AUG 1988. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.

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