Five things we like: Yamaha 90hp four-stroke outboard

We covered many of the finer details and features of Yamaha's F90 four-stroke outboard alongside its F75 twin in our launch review and video back in 2017, but almost two years on, we think it is timely to revisit these popular engines, to re-examine some of their key selling points.

The F75 and F90B were both important new model releases for Yamaha. Their 80hp and 100hp predecessors were getting long in the tooth, and losing sales to rival models that were lighter in weight and higher in tech. More significantly, Yamaha did not have a 90hp four-stroke engine in the Australian line-up.

There was an F90A available to overseas markets, but locally we had to make do with the 1.6-litre F80 and F100A, leaving a hole in the Yamaha line-up that rival manufacturers had been taking full advantage of for many years.

The absence of a 90hp four-stroke outboard had been hurting Yamaha in Australia for more than a decade, so it was crucial for the new F90B to be well received by Yamaha dealers, boaters and anglers around the country.

Yamaha was never going to make a dud engine, so the success of the two new four-stroke outboards was never really in doubt.

Fast-forward almost two years, and the solid sales numbers and thousands of happy customers have confirmed the strength of this engine.

The F90B is proving especially popular. On waterways throughout Australia, you'll find the Yamaha F90B powering everything from big, tiller-steer open boats through to centre and side console fishing tinnies, runabouts, cuddy cabs, pontoon boats, and more.

So why is this new Yamaha proving such hit? Well, we can give you plenty of reasons but here's our top five.

The Yamaha F75/F90 is an in-line four cylinder, 16 valve single cam engine with a 1.8-litre capacity, up from the 1.6 litres of the previous-generation model. With a larger displacement you would expect stronger overall performance, but even we were surprised by the improvement in power and acceleration of the new engine over its predecessor.

Yamaha says the F75/F90 has more power at the top end and more low-down torque. Following our own tests, we would have to concur. The new engine has more grunt throughout the rev range, but particularly down low, making for quicker hole shots and excellent mid-range throttle response.

The Yamaha F90B certainly outperforms the old F100, and we'd go as far as saying that this sweet little engine is more punchy and powerful than most of its rivals.

The F75/F90B has the same 1.8-litre engine capacity as the larger Yamaha F115B, but uses a single overhead cam (SOHC) cylinder head (actuating four valves per cylinder) instead of the larger outboard's double overhead cam (DOHC) layout. This saves weight, and reduces the size of the engine with little compromise to performance.

By adopting the SOHC engine configuration Yamaha was able to reduce the dry weight (no oil or propeller) of the F75/F90 twins to just 162kg. This is about 10kg lighter than the previous-generation model, bringing the new engine into line with comparable four-strokes from rival brands Mercury and Honda.

The Suzuki DF90 remains the lightest of the current four strokes at 155kg. The overall lightest 90hp outboard (ignoring traditional two-strokes) is Evinrude's featherweight 1.3-litre E-Tec 90hp direct fuel injection engine at around 145kg, followed by the Tohatsu TLDI 90hp two-stroke at 153kg. All three have a smaller engine capacity than the Yamaha F75/F90.

Good power and performance often comes with increased fuel use, and yet Yamaha have managed to ramp up the power and torque from the new engines whilst boosting fuel efficiency by a claimed 10 percent over the older model.

The improvement has come about through a redesign of the combustion chamber and the use of lean fuel burn technology that conserves fuel in the critical mid-range.

Whist it is not really possible for us to confirm Yamaha's precise fuel economy percentage gains, we can tell you that the F90 is miserly on fuel. On three different boats (Stabicraft 1600 Fisher Carbon, Horizon 485 SunRunner, and the Stessco 520 Bowrider) the F90 burned between 10.5-11.2L/h at 3500rpm, yielding a remarkable efficiency level of between 1.63 and 1.83 nautical miles travelled for each litre of fuel used.

Most modern four-stroke engines are smooth and quiet, at least relative to the older style two-strokes, and the new F75/F90 is no exception. At idle it purrs quietly in the background, the sound barely audible from the helm station. If it wasn't for the water tell-tale streaming out the back of the cowling you would not know it was running.

Underway, the Yamaha is also very smooth and quiet. There is virtually no powerhead vibration and you can have a normal conversation with crew members without having to raise your voice to be heard.

Measures Yamaha has taken to dampen engine noise include a redesign of the muffler, the addition of an inlet silencer and a revised, more rigid engine mounting system.

Yamaha's Variable Trolling RPM switch is available on several  models throughout the range, but it is great to see it is an option for the F90B. It can be selected if the outboard is equipped with Yamaha's multifunction tiller handle, with the Command Link engine display, or with the new remote switch.

The Variable Trolling RPM feature is great for low-speed lure trolling when fishing for trout, perch, bass and other impoundment species, as well as flathead, bream, tailor and more in coastal waters.

With this clever feature, skippers can dial the idle speed up or down in 50rpm increments. The engine idle speed can adjust from a low of 550rpm through to a high of 1000rpm, thereby allowing an angler to run the boat at a speed to suit the action and presentation of individual lures.

Okay, that's the top five things we like about Yamaha's superb F75/F90 four-stroke engine, but there are plenty of other reasons for its popularity and success.

Some of the other great features include a larger 35-amp alternator (with 28 amps delivered at 1000rpm), NMEA-2000 compatibility (for external displays), compatibility with Yamaha Command Link digital displays and a broad range of Yamaha propellers (some equipped with Yamaha's Shift Dampener System for smoother gear shifts), an offset crankshaft for improved efficiency, a more compact power trim and tilt system, and engine mounting holes that are compatible with other brands for easier repowers.

The Yamaha F75 and F90 outboard engines are available from dealers throughout Australia. Pricing starts from $12,860 and $14,500 (plus installation) respectively.

Specifications: Yamaha 75 - 90hp
Engine type: Four-stroke SOHC 16-valve
Cylinders: In-line four-cylinder
Fuel delivery: Electronic fuel injection
Weight: 162kg (dry, lightest model)
Displacement: 1832cc
Bore x stroke: 81.0mm x 88.9mm
Operating range: 5000–6000rpm
Shaft length: 508mm (20-inch), 635mm (25-inch),
Alternator: 35 amp
Trim method: Power trim/tilt
Gear ratio: 2.15:1
Oil capacity: 3.2L
Emissions rating: CARB 3 star
Servicing: Annually, or every 100 hours after first service
Warranty: Four years, unlimited hours

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