Honda BF90 outboard motor review

The Honda BF90 outboard motor may be most suited for smaller boats, but mid-range fuel efficiency is spectacular.

Compared to some of its newer competition, the Honda BF90 outboard motor is very light on piston displacement. Straight from the Jazz car, the high-revving engine has VTEC or variable intake valve timing that operates only above 5200rpm, so pushing hefty loads is definitely not what this marine engine was designed to do.

Combine this complexity with BLAST and ECOmo technology and you’ll have to develop a very good relationship with your local outboard mechanic! BLAST increases the air/fuel ratio from the normal 14.7:1 to 12:1 for better holeshot performance. ECOmo leans out the ratio to 18:1 under moderate load conditions, such as when the hull is planing cleanly in the 2000 to 4500rpm range and depending on the throttle opening. Above this, the air/fuel ratio reverts to 14.7:1.

So to get the best from the small, complex outboard motor that is the Honda BF90, it should only be fitted to hulls such as lightweight bass boats that plane easily and allow the engine to rev right out.

HONDA BF90D

The Honda BF90 outboard motor has double overhead camshafts to operate the 16 valves and the timing belt should be checked annually for any damage. Some DOHC engines are non-interference, so should the belt break the valves won’t contact the piston crowns (ouch!), but I wouldn’t put it to the test by forgetting to check the belt and change it every 800 to 1000 hours. At least valve clearance is easily done using a feeler gauge and 10mm spanner. But as the engine has a long piston stroke I’d limit maximum cruising rpm to 5000 to avoid unnecessarily high piston speeds.

The 44amp voltage regulated under-flywheel alternator produces up to 35amp of dedicated battery charging current, so the Electronic Control Unit and injectors are not energy guzzlers like some of the competition. The rpm limiter cuts in at 6500.

Powerhead access is good with the fuel filter and canister oil filter easily reached. Being a car engine the flywheel is at the bottom when the engine is upended for outboard duty leaving just the cover for the ignition and alternator. The sump capacity of 4.4lt is adequate for absorbing oil sludge (from dilution) between changes that occur during extended low-speed operation such as trolling. Just a fact of life when owning a raw-water-cooled four-stroke! Honda Marine SAE10W30 oil suits most ambient temperature ranges and is the recommended oil for this engine.

Servicing intervals are every 100 hours or annually after the first 20 hours and the recreational-usage warranty is five years.

ON THE WATER

As my tinnitus slowly gets worse I’m glad there are more four-strokes out there. I can test an engine and not come home afterwards with my ears ringing as was the case after big carbie two-strokes. And like all multicylinder Honda outboards, the Honda BF90 outboard motor was no exception.

Unusually, Honda MPE had mounted the demo Honda BF90 outboard motor on an aluminium Makocraft Estuary Tracker 480 fitted with Minn Kota bowmount and two hefty deep cycle batteries. Honda MPE’s Darren Millgate, a long-time raceboat driver, had chosen a 22in pitch stainless steel Solas prop and mounted the engine high on the transom. While this limited holeshot acceleration, from 5000rpm to wide open throttle, it was stunning for a four-stroke 90.

As expected the demo engine started instantly hot or cold and didn’t blow any oil smoke, nor was there any smell backing upwind. The Honda remote control box had a smooth shifting action (one of the better boxes) and trolling along the engine was almost vibration free. If you want flab reduction, don’t buy this engine.

Pushing a total of 1000kg including a full fuel tank and Darren and me, due to its high mounting the engine was a slug getting us out of the hole and through tight turns at 4000rpm had to be trimmed right in to prevent prop ventilation. But in a straight line the leg could be trimmed right out without blow out, amazing in a tinny! On this hull the Honda had comparable performance to a DFI two-stroke without the noise penalty.

THE TRADE-A-BOAT VERDICT

One of the few benefits of using a marinised car engine in an outboard is that the engine is already clean enough to meet strict automotive exhaust emission laws, and the Honda BF90 outboard motor has some of the lowest emission levels of any 90hp outboard. So it easily gains an ODEA 3-Star rating.

Another benefit is that spare parts for the powerhead are available from Honda car dealers and they should be cheaper than dedicated marine parts.

Visit Honda Marine for more information.

HONDA BF90 SEA TRIALS

Average of two-way runs on the Gold Coast Broadwater, calm water.

RPM	SPEED (KTS)	FUEL BURN (LT/H)	LT/NM
750 (trolling)	2.3	1	2.3
2800 (planing)	14.6	8.4	1.7
3000 (slow cruise)	16.3	8.5	1.9
4000 (cruise)	25.4	9.6	2.6*
5000 (max cruise)	33.5	18.3	1.8
6200 (WOT)	43.3	27.5	1.6

* Note the incredible midrange fuel efficiency. Performance data supplied by the author.

HONDA BF90D SPECIFICATIONS

Honda BF90 price: $A14,900

TYPE Four-cylinder four-stroke petrol outboard

RATED BHP/MHP* 88.7/90 at 5800rpm

REC. WOT RANGE 5300 to 6300

DISPLACEMENT 1496cc

BORE X STROKE 73 x 89cc

GEAR RATIO 2.33:1

WEIGHT 162kg

WARRANTY 5 years

* Brake horsepower/metric horsepower

COMPARED: COMPETING OUTBOARDS

SUZUKI DF90
WEIGHT	155kg
BHP/MHP	88.7/90 at 5800rpm
DISPLACEMENT	1502cc
SUZUKI DF90 PRICE	$POA
WARRANTY	5 years
OEDA STARS	3