Tohatsu M70C

All of Tohatsu's carbie two-stroke outboards perform better in their uprated form than when de-rated and the M70C is no exception.

Like the de-rated M60C, in its current form the 70 was released on the Aussie market in 1998 and features the same gearcase torpedo size as the M90A but a much deeper gear ratio. This allows engine torque to be more effectively converted to thrust when pushing aluminium runabouts up to five metres than would a smaller-ratio box.

The M70C has Tohatsu's "dual swirl" combustion chamber design to comply with current US EPA exhaust emission regulations for carburetted two strokes. Of course the M70C, like every other carburetted two-stroke outboard, doesn't meet US EPA 2006 regulations, but due to its popularity it's likely this model will be available in Australia for several years to come.

Tohatsu's automixing oil injection system is standard. Oil is injected at the fuel pump, ensuring the carburettor throttle butterflies receive lubrication and eliminating the need for small diameter, separate oil delivery lines per cylinder which can clog from gelling should different types and/or brands of oil be mixed together. To ensure fuel doesn't go stale in the carbies during extended periods of disuse Isopropyl Alcohol can always be mixed with the petrol.

The M70C also scores over its direct Yamaha competition with voltage-regulated alternator whereas the 70B has only an 80W unit that really is inadequate for the amount of electronics fitted to most serious amateur fishing boats. But the M70C is more of a first generation outboard than the 70B and has an electric choke system instead of a cold start fuel primer. Simply turning the ignition key on the Yammie ensures instant starting hot or cold but Tohatsu's system requires careful co-ordination of the fast idle lever and choke control to easily start the motor. However Tohatsu's choke system is inherently more reliable and easier to service.

Mounted on a Blue Fin 475 Weekender runabout and spinning a 15-inch pitch Tohatsu alloy prop, the demo M60C provided plenty of power for our two-adult load, which brought the total displacement to 780kg. Cold starting was a bit quirky but once running the M60C warmed quickly from cold and running on a 50:1 break-in mix of ULP and TC-W3 Quicksilver oil in addition to the oil injection, oil smoke appeared only below 2000rpm. Unlike the M60C the 70 had no "chugginess" at trolling revs, even when cold and across the entire rev range noise and vibration levels were similar to the 70B. Power astern was good providing the antiventilation plate was kept at least three quarters immersed.

Trolling at 750rpm the demo M70C averaged 5.3km/h and planed us cleanly at 26.2km/h and 3200rpm. Cruising quietly at 4000rpm the averages were 36.1km/h and 11.5lt/h and through full-lock figure of eight turns at these revs no propeller ventilation occurred despite the leg not being trimmed right in.

But what really set the 70 apart from the M60C was the acceleration when the throttle lever was "floored" at 4000rpm. There was an almost instantaneous jump to 5000rpm with the wide open throttle averages being 55.6km/h and 27.6lt/h at 5800rpm, right where the engine should reach to allow for heavier loads such as when carrying a family of four and associated gear. Surprisingly for a carbie two-stroke we could hold a normal conversation at the helm.

Servicing the M70C is straightforward with very good powerhead access and separate bowl-type fuel and oil filters fitted. The recommended servicing intervals are every 50 hours or six months after the first 10 hours and the waterpump impeller should be replaced every 100 hours or yearly.

The M70C is well engineered and very good value for saltwater anglers who need cost-effective power for tinnies to five metres. The warranty coverage is three years for recreational usage.