Honda BF75D

Considerate clout

Released on the Aussie market in September 2006, the current model BF75 is based on the Honda Jazz car engine and is a de-rated version of its BF90 counterpart that also has VTEC or variable intake valve timing.

Although it has a six per cent smaller piston displacement than its four-carbie SOHC 12-valve BF75 predecessor (based on the Honda Civic car engine), the current model is a vastly better engine and incorporates the features of the multipoint EFI Honda BF50.

These include BLAST or Boosted Low Speed Torque where, depending on throttle opening, the ignition timing is advanced to develop more horsepower and torque to quickly plane a hull.

And by utilising an 02 (oxygen) sensor in the exhaust system the air/fuel ratio is leaned out to 18:1 in the 2000 to 4500rpm range, again depending on throttle opening, instead of the normal 14.5 to 14.7:1 ratio of carbie engines. This gives the EFI BF75 up to 30 per cent better fuel efficiency than its predecessor.

Another feature of the current BF75 is the three-way cooling system, where the cylinder head thermostat opens at 50°C, the cylinder block thermostat at 60°C and the exhaust manifold has direct cooling. This system maintains consistent temperatures under high loads and increases powerhead longevity.

The alternator output has been increased from 20 to 44amp with up to 35amp for dedicated battery charging.

Via the Engine Alert System, the Electronic Control Unit constantly monitors engine coolant overheating, low oil pressure, over-revving (6500rpm), water in the fuel system and battery condition, as effective ECU operation is dependant on a healthy battery.

However, unlike the BF50, the BF75 has an in-line crankshaft and driveshaft with a single gear reduction in the lower unit.

EASY RIDING HONDA
Spinning a 17in prop and mounted on a Stacer 489 Easy Rider, the demo BF75 (below)was almost as quick out of the hole as an Evinrude E-TEC 75 tested on a Stacer 475 Bay Master Sports runabout in 2003, and with the throttle floored from trolling revs, it planed us in three seconds.

The 489 was a much better choice of hull for the BF75 than the Quintrex 470 Coast Runner used for the BF50 test and allowed the BF75 to plane at the lower end of the lean burn zone for improved midrange fuel efficiency.

Pushing 950kg, including two adults and a full fuel tank, the BF75 trolled with hardly any vibration at 4.1kmh and 750rpm using 1.0lt/h and achieved a clean plane at 23.4kmh and 3000rpm.

The most economical cruising was at 4000rpm with averages of 40.1kmh and 9.3lt/h, and through a full-lock figure of eight turns no prop ventilation occurred.

At my recommended maximum cruising rpm of 5000 the averages were 51.8kmh and 17.7lt/h, while at WOT and 6100rpm we averaged 64.6kmh and 23.9lt/h. In comparison, the Stacer 475/E-TEC 75 combo with a displacement of 860kg averaged 68.5kmh and 25.2lt/h at 5150rpm spinning a 17in prop, so considering the additional weight the BF75 was on par with the E-TEC for performance. At or near WOT, noise levels were lower than the E-TEC and we could talk normally at the helm.

The demo BF75 started instantly hot or cold with no smoke appearing at any time, nor was there an oil smell backing upwind. Providing the antiventilation plate was kept at least three-quarters immersed, power astern was good with no cooling water starvation. The Honda remote control box had a positive yet smooth action when shifting into forward or reverse.

Powerhead access is excellent, with the oil dipstick and oil filter easily reached. Servicing intervals are every 100 hours, or annually after the first service at 20 hours.

The BF75 has the lowest HC, oxides of nitrogen and CO emissions of any four-stroke in its power range and meets the OEDA 3-Star emissions rating. Warranty is five years for recreational usage.