Released in April, the TLDI 90 is based on the three-cylinder M90A released locally in 1987.

The TLDI 90 has all the features of its smaller TLDI 50 counterpart, such as Orbital direct fuel-injection and electronic engine management. The Orbital Combustion Process utilises six injectors, three of which inject air into the fuel rail at 90psi. Mixed with fuel pressurised to 70psi, the fuel/air mix is then injected via the other three injectors directly into the combustion chambers.

A single throttle body air-intake incorporates Throttle Position Sensors for load and barometric pressure (to ascertain the correct air/fuel ratio) and along with the air, lubricating oil is carried via the crankcase to the combustion chamber. The oil is injected at the reed valves like Yamaha's 'Precision Blend' system, and Tohatsu Corporation claim the fuel/oil ratios vary from 50:1 at Wide Open Throttle (WOT) down to 450:1 at Dead Slow Troll (DST).

To diagnose engine operating problems a total of 28 troubleshooting codes are provided, indicated by various combinations of the three warning lights in the analog tachometer. This system allows a servicing technician to work out where the problem lies without needing a laptop computer.

To break-in a new or reconditioned motor, all Tohatsu dealers have to do is 'force-feed' the engine oil for the first half-hour, achieved by resetting the oil pump control lever and running the engine at idling speed in a test tank. Owners then follow the normal 10-hour break-in procedure.

With the TLDI 90 being aimed specifically at the 90hp four-strokes, the Australian distributor for Tohatsu, Lakeside Marine, went to the trouble of setting up a TLDI 90 on a Signature 520C. This allowed me to directly compare the motor with a Mercury F90 I had tested on a 520R and although the 520C weighs 25kg more than the 520R, this was compensated by the 18% lighter weight of the TLDI 90.

Spinning a 15-inch stainless steel Power Tech prop and pushing a total of 920kg (including two adults), the TLDI 90 trolled at 4.1kmh on 700 revs consuming 0.7lt/hr and at 900 revs it averaged 6.0kmh using 0.8lt/hr. In comparison, spinning a 14-inch Quicksilver Vengeance prop and pushing 920kg, the F90 trolled at 3.9kmh on 700 revs using 1.2lt/hr but with lower vibration levels.

The TLDI 90 achieved a clean plane at 25.6kmh on 3000 revs, whereas the F90 planed us at 22.2kmh on 2900 revs. At steady cruising revs of 4000 the TLDI 90 averaged 40.9kmh consuming 12.8lt/hr, while the F90 averaged 45.5kmh using 10.5lt/hr. And through tight figures of eight at 4000 revs the F90's prop refused to ventilate, whereas the Power Tech prop let go even with the leg trimmed right in.

At WOT the TLDI 90 averaged 58.9kmh on 5600 revs consuming 27.6lt/hr and the F90 averaged 66.0kmh on 5300 revs using 28.0lt/hr, but the Tohatsu was quieter than the Merc which, like most four-strokes, started to become relatively noisy over 4000 revs. There was no difference in vibration levels at WOT despite the Merc having another cylinder.

As with the F90, the TLDI 90 started instantly cold but much faster hot and shifting in or out of gear was slightly smoother at the same revs. The Tohatsu also had the unique setting of trolling revs, where simply pushing in the ignition key increases the revs by 100 at a time out to 900. Providing the antiventilation plate was kept immersed, the TLDI 90 had comparable power astern and no cooling water starvation occurred. No oil smoke appeared at any time.

Servicing the TLDI 90 is straightforward and Lakeside recommends intervals at every 50 hours or six months after the 10-hour service.

While the TLDI 90 doesn't provide the mid-range fuel efficiency of the F90, it scores at trolling speeds where it actually uses less fuel than a four-stroke Merc F50. And because it is a two-stroke it can be operated for extended periods at WOT, whereas I wouldn't contemplate this with the automotive-based F90!