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Tohatsu M3.5B two-stroke (74.6 cc, forward/neutral shift) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu M3.5B two-stroke (74.6 cc, forward/neutral shift) (3.5 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Tohatsu M3.5B, model number 3F0. 1 cylinder, 74.6 cc (4.6 cu in), bore 47 x stroke 43 mm, 2.58 kW (3.5 PS) at 4750 rpm, full throttle range 4200 to 5300 rpm, gasoline/oil mixture (gasoline 50 : oil 1), water cooled by rubber impeller, recoil start, pointless CD ignition magneto, 1.4 L integral tank, dog clutch forward and neutral, gear ratio 13:28. Premix, no oil injection.

Quick answers

What two-stroke oil does a Tohatsu M3.5B two-stroke use?
Genuine engine oil or any NMMA certified TC-W3 two-cycle outboard oil.
What is the fuel to oil ratio for a Tohatsu M3.5B two-stroke?
Gasoline 50 : oil 1.
What gear oil does a Tohatsu M3.5B two-stroke use, and how much?
TOHATSU gear oil (GL-5, SAE #80 or #80W). Quantity: Approx. 180 cc.
What spark plug does a Tohatsu M3.5B two-stroke use?
NGK BP6HS-10 or Champion L87YC10, qty 1. Gap: 0.9 to 1.0 mm; limit 1.25 mm.
How often should a Tohatsu M3.5B two-stroke be serviced?
The factory schedule lists: Initial 10 hours; Every 30 hours; Every 50 hours; Every 100 hours; Every 200 hours. 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 M3.5B 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 M3.5B two-stroke?
1100 rpm in gear, 1300 rpm in neutral.
What is the propeller nut torque on a Tohatsu M3.5B two-stroke?
Held by a split pin.

Maintenance specs

Two-stroke oilGenuine engine oil or any NMMA certified TC-W3 two-cycle outboard oil
Fuel to oil mixGasoline 50 : oil 1
Gear oilTOHATSU gear oil (GL-5, SAE #80 or #80W)
Gear oil quantityApprox. 180 cc
Gear oil upper and lower oil plugs2 plugs (oil plug upper, oil plug lower).
Spark plugNGK BP6HS-10 or Champion L87YC10, qty 1
Spark plug gap0.9 to 1.0 mm; limit 1.25 mm
Spark plug torque2.5 to 3.0 kg-m (14 mm)
Idle speed1100 rpm in gear, 1300 rpm in neutral
Fuel pipesMust be replaced every two years
AnodesGear case anode: check for wear and deformation every 100 hours; replace without delay
PropellerHeld by a split pin

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

  2. Every 30 hours

    Replace: gear case plug gaskets

    Check: spark plugs

  3. Every 50 hours

    Replace: gear case plug gaskets

    Check: gear case oil

  4. Every 100 hours

    Replace: gear case plug gaskets

    Check: gear case oil, water pump impeller, anodes

  5. Every 200 hours

    Replace: gear case oil, gear case plug gaskets, water pump impeller

    Check: anodes

Source: Tohatsu M3.5B service manual, MAR 1992. 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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