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Tohatsu M120A / M140A and M115A (4 cylinder, 1,768 cc, carbureted two-stroke) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu M120A / M140A and M115A (4 cylinder, 1,768 cc, carbureted two-stroke) (115 to 140 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: M120A and M140A, remote control. 4 cylinders, 1,768.8 cc (107.94 cu in), bore 88 x stroke 72.7 mm, 4 carburetors, reed valves; M120A 88.3 kW (120 PS), M140A 103 kW (140 PS), full speed range 5,200 to 5,700 rpm; gear ratio 13:26; auto mixing with an integral oil tank.

Quick answers

What two-stroke oil does a Tohatsu M120A / M140A and M115A use?
Tohatsu genuine 2-cycle engine oil Super Gold.
What is the fuel to oil ratio for a Tohatsu M120A / M140A and M115A?
Auto mixing system: 50:1 to 120:1, set by the oil pump. During break-in also a 50:1 mix in the fuel tank.
What gear oil does a Tohatsu M120A / M140A and M115A use, and how much?
Tohatsu genuine gear oil. Quantity: Approx. 900 cc.
What spark plug does a Tohatsu M120A / M140A and M115A use?
NGK B8HS-10 or Champion L78C, qty 4. Gap: 0.9 to 1.0 mm (0.0354 to 0.0394 in).
How often should a Tohatsu M120A / M140A and M115A be serviced?
The factory schedule lists: Initial 10 hours or 1 month; Every 50 hours or 3 months; Every 100 hours or 6 months; 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 M120A / M140A and M115A?
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 M120A / M140A and M115A?
Trolling 550 to 750 rpm; idling adjustment after synchronizing the 4 carburetors: pilot screw 1 5/8 ± 1/4 turns, 700 to 850 rpm with the clutch at F.
What is the propeller nut torque on a Tohatsu M120A / M140A and M115A?
29.4 to 39.2 N·m (3.0 to 4.0 kg-m, 21.69 to 28.92 lb-ft).

Maintenance specs

Injection (two-stroke) oilTohatsu genuine 2-cycle engine oil Super Gold
Fuel to oil ratioAuto mixing system: 50:1 to 120:1, set by the oil pump. During break-in also a 50:1 mix in the fuel tank
Gear oilTohatsu genuine gear oil
Gear oil quantityApprox. 900 cc
Spark plugNGK B8HS-10 or Champion L78C, qty 4
Spark plug gap0.9 to 1.0 mm (0.0354 to 0.0394 in)
Spark plug torque24.5 to 29.4 N·m (2.5 to 3.0 kg-m, 18.1 to 21.7 lb-ft)
Trolling / idle speedTrolling 550 to 750 rpm; idling adjustment after synchronizing the 4 carburetors: pilot screw 1 5/8 ± 1/4 turns, 700 to 850 rpm with the clutch at F.
ThermostatWax type with pressure relief valve: opens at 60 °C, opens fully at 70 °C (158 °F).
AnodesTrim tab, cylinder head and stern bracket: inspect every time used, replace if wear is 30% or greater; remark "Every year"
Propeller nut29.4 to 39.2 N·m (3.0 to 4.0 kg-m, 21.69 to 28.92 lb-ft)
Power trim and tilt fluidATF oil, for example Shell Dexron-II, Esso ATF, Mobil DTE #22. Tilt up, set the tilt stopper, remove the oil plug and check the oil is just below the oil plug hole

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 or 1 month

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

    Check: spark plugs, fuel filter

  2. Every 50 hours or 3 months

    Replace: gear case plug gaskets, propeller cotter pin

    Check: spark plugs, fuel filter, gear case oil

  3. Every 100 hours or 6 months

    Replace: gear case plug gaskets, propeller cotter pin

    Check: spark plugs, fuel filter, gear case oil, water pump impeller, thermostat

  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, thermostat, anodes

Source: Tohatsu M120A/M140A service manual. 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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