Honda BF20 four-stroke

Although Honda is not the first company to make a 20hp four-stroke (Yamaha has had a 20hp version of its F25A for about five years in markets outside of Australia), what sets the BF20 apart from existing 20-25hp four-strokes is its light weight.

Through the extensive use of plastics, even on the tiller arm, Honda has achieved a manual start shortshaft weight of only 46.5kg, 5kg less than Tohatsu's 328cc 18hp four-stroke.

A front-mounted gearshift is fitted and electric start models retain the overhead manual recoil starter with a tiller arm starter button near the twistgrip throttle, which also incorporates a throttle friction adjuster.

The steering friction adjuster has a slide control, similar to Tohatsu's MFS 18B.

The BF20 has automatic decompression starting, a rev limiter and automatic reduction of revs or complete engine shutdown should the engine overheat or oil pressure fail.

Honda also offers optional power tilt, although the BF20 cannot be trimmed out when planing due to the hydraulic ram's inability to handle the prop thrust.

Up to about 2000rpm the motor can be trimmed out to achieve a shallow water drive setting, but as with Tohatsu's four-stroke MFS 25A/30A, the power tilt system should have been engineered to handle trimming in or out across the entire rev range.

The automatic choke system eliminates the cold-start guesswork needed with manual chokes. Manual start models have a voltage-regulated 6-amp alternator and electric start models have a 12-amp unit that still produces 8 amps at only 2000rpm.

Both demo motors performed very well on hulls that really should have been fitted with 25hp outboards. They started instantly hot or cold, warmed quickly from cold and had the lowest vibration levels of any twin-cylinder four-stroke I've tested yet.

Using the manual recoil starter, a firm two-hand pull was needed to fire up the engine when cold, but only needed a light one-hand tug when warm.

The remote-control shift feel of the electric-start power tilt model was excellent with rapid tilting or lowering when needed.

However, when both motors were left for about 15 minutes then re-started, they sometimes needed some extra throttle to overcome vapour lock, unlike the MFS 18B. But at no time did the Hondas blow any oil smoke and, providing the anti-ventilation plate was kept immersed, power astern was good.

The first motor was mounted on a Sea Jay 3.9 Nomad Deluxe vee-nose punt and spun a 10in pitch alloy prop pushing a total of 420kg including two adults and test equipment.

The BF20 trolled at 3.2kmh and planed cleanly at 21.5kmh. The WOT average was 37.5kmh and only through tight figure-eight turns at WOT did any prop ventilation occur.

The second motor was on a Stessl 385 Edge Tracker side console vee-nose punt. Spinning a 9in four-blade alloy prop and pushing a total of 510 kilos including two adults and test equipment, it trolled at just 3.0kmh on 900rpm using 0.4lt/hr.

With my co-driver sitting forward to get us out of the hole and with the throttle wide open, we planed at 20.0kmh. Throttled back to 5000rpm to maintain a clean plane the BF20 consumed 4.9lt/hr with the co-driver sitting amidships. At WOT the BF20 averaged 35.0kmh on 5650rpm using 7.0lt/hr. Prop ventilation occurred only through tight figure-eight turns at WOT.

Accessing the BF20 powerhead is very difficult compared to the MFS 18B. To replace the spin-on oil filter or even the spark plugs requires removal of the lower cowl. Recommended servicing intervals are 100 hours or yearly (when the waterpump impeller should be replaced) after the first 20 hours, but I would change the oil and filter every 50 hours or six months.

The warranty coverage is two years for recreational use and the BF20 complies with California Air Resources Board (CARB) 2008 exhaust emission regulations.