Honda BF90

In my review of the Honda BF75, I stated the carburetted models performed better in their de-rated versions (based on testing of all Honda outboards). But having tested the current-model BF90 on two very different hulls, I've found a significant upper-throttle performance gain in this motor over its de-rated BF75 counterpart.

The first boat fitted with the BF90 was a Markham 522 Profish. Measuring 5.25m x 2.25m, this boat has a hull weight of 590kg and a maximum horsepower rating of 150hp. Spinning a 15-inch prop and pushing a total of 970kg (including two adults) the extra-long shaft BF90 trolled at 4.9kmh at 900rpm and maintained 5.4kmh at 1000rpm. At 2000rpm we averaged 9.8kmh and 14.6kmh at 3000rpm.

A clean plane was achieved at 3500rpm and 24.0kmh and by 4000rpm we were cruising at 30.4kmh, consuming a moderate 9.0lt/hr. Another 1000 revs returned a 'fast' cruise of 45.2kmh and the Wide Open Throttle (WOT) average was 58.4kmh at 6200rpm, consuming 28.0lt/hr. The full-throttle revs indicated that the brand-new test motor was underpropped and would have benefited from the fitting of a 17-inch prop.

Despite the use of an alloy prop with minimal blade cupping, there was no ventilation in tight figures of eight at 5000rpm.

The second test motor was a standard longshaft model fitted to a Horizon 5000 Centre Console. This hull measures 5.0m x 2.0m and, like the 522 Profish, has no pod. It has 3.0mm bottom and 2.0mm topside aluminium sheeting. This boat has a bare hull weight of 380kg and is rated to 90hp.

Spinning a 19-inch prop and pushing a total of 900kg (including four adults) the BF90 maintained a steady 4.6kmh on 800rpm (100 lower due to the much larger prop) and at 1000 averaged 7.2kmh. Another 1000 revs increased the average to 11.4kmh and a clean plane was achieved at 24.5kmh at 2800rpms. At 3000rpm we averaged an effortless 28.4kmh, while 4000rpm returned 45.0kmh, again consuming 9.0lt/hr.

At 5000rpm the BF90 averaged 57.0kmh and the WOT average was 62.0kmh at 5300rpm, consuming 26lt/hr. At full throttle it was obvious the motor was slightly overpropped and really needed a 17-inch prop.

Despite the use of an alloy prop and considering the Horizon had a long deep keel, again there was no prop ventilation.

One feature that really surprised me was the ability of the waterpump impeller to pump water with the antiventilation plate half immersed. According to Jim Nicol Honda's service manager, Darren Millgate, it's not uncommon for the impeller itself to last up to 800 operating hours, though he still recommends changing it every 100 hours.

Power astern was good, even with the AVP's partially exposed, and at all speeds the pilot water discharges were clearly visible. Both motors started instantly hot or cold and never blew any oil smoke.

The BF90 is based on the 1.6lt Honda Civic motor, but the twin overhead cams and four-valve head have been swapped for a single overhead cam and three-valve head. There are four carbies and the usual Honda big-motor features of overheat and low oil level/pressure alerts and automatic rev reduction are fitted. A rev limiter is standard and a speedo pickup is incorporated in the lower unit.

Servicing the BF90 is straightforward and recommended intervals are every 100 operating hours or six months after the first 20 hours, where the valve clearance must be checked. I would change the engine oil and filter every six months regardless of how few hours are clocked up - a straightforward task, which costs an owner about $40 in parts.

The BF90 certainly has some stiff competition, such as the Mariner/Mercury F90 and lighter FICHT 90, but because Honda got it right in the first place the BF90 can still give these motors a run for their money. According to owners' interviewed, it has proven reliable and with regular maintenance should provide several thousand hours of boating pleasure.

Ed's note: Trailer Boat's sister magazine BlueWater Boats & Sportsfishing recently sold its twin BF90 Honda powered Pacific Sportsfish project boat 'BlueWater II'. Logging some reasonable hours on the BF90s we can vouch for their trouble-free nature, excellent trolling performance and relative economy at cruise revs.

Noise, or lack of it, is something these engines have over their direct-injection two-stroke counterparts. They are quite amazingly soothing after a day on the water - you can even flush the motors at home without incurring the wrath of the neighbours.

Of the two negatives we can raise, one is touched upon above. Propping is all-important if you want to get the best out of your Honda. Honda's own props are, in a word, average. Mercury props fit or get in touch with Solas and try out one of that company's excellent Titan range of SS props.

The other negative is corrosion resistance. It's our experience Honda needs to work on its coatings and cables. Cosmetic (not damaging or structural) corrosion made some parts of the underside of engines unsightly fairly quickly and Honda's control cables are prone to accelerated wear via the ingress of saltwater. We ended up changing a set of cables for each engine in two years.