Honda BF50D

Honda's head honcho

Originally released on the Aussie market in 1993 as the BF45 then later upgraded to 50hp, the new EFI BF50 is still based on the original powerhead which, with more than 160,000 units sold, has been Honda's biggest selling marine engine.

Unlike models from the BF75 upwards (whose powerheads were originally designed for automotive applications) the BF50 has a purpose-built marine powerhead with the flywheel at the top and not the bottom. The "square" powerhead with the same bore and stroke dimensions also reduces piston speed at higher revs.

The BF50 and its de-rated BF40 counterpart are the only Honda outboards in the entire range to have an offset driveshaft, a feature that Honda pioneered with the BF35/45.

Originally, the gears had a 1:1 ratio but now reduction gearing is used to reduce lower unit size. This means that the BF50 powerhead has a clockwise or right-handed rotation viewed from the bottom of the engine and not the counter clockwise or left-hand rotation of all other Honda outboards.

In the new BF50, Honda has retained the original engine features such as a single belt-driven overhead camshaft with two valves per cylinder making the engine very easy to service.

BLAST BOOST
The previous BF50 had three single-barrel carbies with accelerator pumps, but the new model has sequential multipoint EFI and the clever BLAST or Boosted Low Speed Torque system which richens the air/fuel ratio from the normal 14.7:1 to 12:1 for improved holeshot performance. However, at cruising revs (3000 to 4500) the engine management system leans out the air/fuel ratio to around 18:1 to significantly reduce fuel consumption. This system will be incorporated in more Honda outboards down the track.

Other features include a rev limiter and warning lamps in the instrumentation for EFI system malfunction, low oil pressure, engine overheat and alternator charging malfunction. As with all EFI Hondas from 40hp upwards, the new BF50 can also be fitted with digital fuel flow and range-to-empty instrumentation.

Despite being mounted on a Quintrex 470 Coast Runner runabout and a hull larger than I would recommend for this engine, the demo BF50 from Honda MPE performed very well. It started instantly hot or cold and as expected, didn't blow any oil smoke, nor was there an oil smell when backing upwind. Providing the antiventilation plate was kept immersed power astern was good and the new Honda control cable system provided a light but positive shift ahead or astern.

Pushing a total of 800kg, including two adults and full fuel, and spinning a 13in pitch Honda alloy prop, the BF50 trolled us at an almost vibration-free 3.7kmh and 780rpm using 0.7lt/h. A clean plane was achieved at 22kmh and 3700rpm, although when the throttle was “floored” from trolling speeds the revs quickly jumped to 4500 with the hull planing in less than 10 seconds. Cruising at 4000rpm the averages were 32.4kmh and 7.5lt/h and through a full-lock figure of eight turns at these revs no prop ventilation occurred and the power trim system worked quickly and quietly.

WOT'S THAT?
At my recommended maximum cruising revs of 5000 the averages were 42.9kmh and 15.2lt/h, and at Wide Open Throttle and 5850rpm we averaged 47.9kmh and 18.3lt/h, not bad for a 50 on a hull of this size. At WOT the BF50 was so quiet we could talk normally at the helm and the new model was significantly quieter than the previous BF50 due to the absence of carbie induction roar.

Powerhead access is very good with the engine oil filler cap, oil level dipstick and canister oil filter easily reached. Honda recommends servicing the BF50 every 100 hours or yearly (also for waterpump impeller replacement) after the first service at 20 hours when the valve clearance must be checked.

I would also check the camshaft timing belt every 100 hours for any fraying, although it is designed to last at least 800 hours and should it break, the engine is a non-interference type where the valves won't contact the piston crowns.

The BF50 has an OEDA "3 Star" exhaust emissions rating and a five-year recreational-usage warranty.